How give space text in math mode?

Question

I have a problem about space text in math mode , and i have minimal working anwers like this following from Microsoft Word :

But, since i use LaTeX dont space text in math mode, like this following from LaTeX result :

How give space text math mode in LaTeX ? I use code LaTeX like this

\begin{tabular}{lll}

$Biaya total_{kincir angin}$&=&40 $\times$ Rp 60.000.000,00\\
                          &=&  Rp 2.400.000.000,00
\end{tabular}

and

 \begin{tabular}{lll}

$Biaya total_{kincir angin}$&=& 3000 $\times$ Rp 5.000.000,00\\
                            &=& Rp 15.000.000.000,00
\end{tabular}

Answer 1

\documentclass[preview,border=12pt]{standalone}% change it back to your own document class
\usepackage{amsmath}
\usepackage[
    group-separator=.,
    output-decimal-marker={,},
]{siunitx}

\def\dummy{%
Karl's students do not care about dashing patterns. 
Karl's students do not care about arrow tips. 
Karl's students, by the way, do not know what a transformation matrix is.}

\begin{document}
\dummy
\begin{align*}
\text{Biaya Total}_{\,\text{kincir angin}}
    &= 40 \times \SI{60000000.00}[Rp\,]{}\\
    &= \SI{2400000000.00}[Rp\,]{}
\end{align*}
\dummy
\end{document}

Remarks:

• always specify your decimal numbers with a period as the decimal marker.
• always use siunit when specifying numbers such that you can change the setting globally.
• group-separator=. makes the input 123456 get rendered as 123.456.
• output-decimal-marker={,} makes the input 12.23 get rendered as 12,45.
• Combining both group-separator=.,output-decimam-marker={,} makes the input 123456.78 get rendered as 123.456,78.
• use align* to vertically align the =s and to remove the equation numbers.
• use \text in math mode to make texts get rendered as normal texts.

Answer 2

The math italic font is not designed to make multi-letter words, the letters are widely spaced to producing spacing fro individual identifiers. Use

\textit{Biaya total}_{\textit{kincir angin}}

Together with the amsmath package so that the \text... commands produce smaller fonts