Since they are simmilar we will then have the following relationships.
[tex]\frac{15}{10}=\frac{9}{x}[/tex]
Now, we solve for x, as follows:
[tex]x=\frac{9\cdot10}{15}\Rightarrow x=6[/tex]
The expression goes along the lines of. 15 is to 10 what 9 is to x, with this as was done we solve for x and determine it's value, that since they keep proportionality.
