Sonya can walk 12 kilometers in 4 hours. if she has to walk 15 kilometers, how much time will it take her?

First, We Should Find The Unit Rate...
12 kilometers

    4 hours
We Need To Simplify. 12/4 Can Be Simplified To 3/1. So, 3 kilometers/1 hour is the unit rate. Now, We Need To Change It To 15/X. 
15       3
 =
 X        1
Solve For X. To Solve, Multiply Means And Extremes. The Equation Becomes: 
3X = 15*1.
Simplify.
3x = 15.
Now, Divide Both Sides By 3.
X = 15/3.
15/3 = 5. 
X = 5.
So, Sonya Can Walk 15 Kilometers In 5 Hours. :D