The answer is 2.
3x+2y=3
2x-2y=7
solve both the equations
3x+2y=3
+2x-2y=7
5x=10
so we get
x=2
Notice the picture below
the lateral area, or just the area of the sides, well, the sides are really just 4 triangles, so just get the area of each, and sum them up, that's the lateral area
V = x/t = 4.5 mil / 3 h = 1.5 mph
Since, v = 1.5 mph (or we can say that v is constant), distance and time vary directly and the constant of variation is 1.5 mph.