Answer:
[tex]\boxed{\tt 36 \ minutes}[/tex]
Step-by-step explanation:
Let's make a proportion using the following setup:
[tex]\frac{minutes}{kilometers} =\frac{minutes}{kilometers} \\[/tex]
We know it takes Billy 6 minutes to walk 1.5 kilometers.
[tex]\frac{6\ minutes}{1.5\ kilometers} =\frac{minutes}{kilometers}[/tex]
We don't know how long it takes him to walk 9 kilometers, so we can say it takes him x minutes to walk 9 kilometers.
[tex]\frac{6\ minutes}{1.5\ kilometers} =\frac{x\ minutes}{9\ kilometers}[/tex]
[tex]\frac{6}{1.5} =\frac{x}{9}[/tex]
Now, solve for x. To do this, isolate x on one side of the proportion. x is being divided by 9. The inverse of division is multiplication. Multiply both sides of the proportion by 9.
[tex]9*\frac{6}{1.5} =\frac{x}{9}*9[/tex]
[tex]9*\frac{6}{1.5} =x[/tex]
[tex]9*4=x[/tex]
[tex]36=x[/tex]
x= 36 minutes
It will take Billy 36 minutes to walk 9 kilometers.
