I just want to make "for N = 1" and "for N = 2" left justified. How can I manage this?
\begin{multline}
\begin{aligned}
\underline{\textbf{for N = 1:}}& \\ \Big\{ 1 -\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{2}^k - 4\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{1}^k - \lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{0}^k + 2\lambda_2 \left(\prescript{}{l}{\delta}_{1}^k\right)^3\Big\}\textcolor{red}{\boldsymbol{\prescript{}{l+1}{\delta}_{1}^k}} + \\ \Big\{ 2\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{2}^k + 4\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{1}^k + 2\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{0}^k - 2\lambda_2 \left(\prescript{}{l}{\delta}_{1}^k\right)^3\Big\}\textcolor{red}{\boldsymbol{\prescript{}{l+1}{\delta}_{2}^k}} + \\ \Big\{ -\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{2}^k - \lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{0}^k \Big\}\textcolor{red}{\boldsymbol{\prescript{}{l+1}{\delta}_{3}^k}} = \textcolor{blue}{\boldsymbol{\delta_{1}^{k-1}}}
\\
\\
\\
\underline{\textbf{for N = 2:}}& \\ \Big\{ 1 -\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{2}^k - 4\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{1}^k - \lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{0}^k + 2\lambda_2 \left(\prescript{}{l}{\delta}_{1}^k\right)^3\Big\}\textcolor{red}{\boldsymbol{\prescript{}{l+1}{\delta}_{1}^k}} + \\ \Big\{ 2\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{2}^k + 4\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{1}^k + 2\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{0}^k - 2\lambda_2 \left(\prescript{}{l}{\delta}_{1}^k\right)^3\Big\}\textcolor{red}{\boldsymbol{\prescript{}{l+1}{\delta}_{2}^k}} + \\ \Big\{ -\lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{2}^k - \lambda_1 \left(\prescript{}{l}{\delta}_{1}^k\right)^3 \prescript{}{l}{f}_{0}^k \Big\}\textcolor{red}{\boldsymbol{\prescript{}{l+1}{\delta}_{3}^k}} = \textcolor{blue}{\boldsymbol{\delta_{1}^{k-1}}}
\label{SingleDropletEqns}
\end{aligned}
\end{multline}