Can someone explain how this problem is solve? i'm not understanding how they came up with 4.

Since the denominator is 9 and they multiplied it by 4, the numerator;5 also needs to multiply by 4. 

Same thing with this: If the denominator is 9 and they multiplied by 8, the numerator is also must be multiplied by 8

It's 4 because 9 times 4 equals 36

Ucan draw that on a graph sheet and count the no. of units and apply the area formula of rectangle