ANSWER :
Base : 15 inches
Height : 4 inches
EXPLANATION :
Recall the area formula of a triangle :

The area of the triangle is 30 in^2
The base is 3 inches more than 3 times the height so :

Using the formula above :

Equate the factors to 0.
h + 5 = 0
h = -5
h - 4 = 0
h = 4
Since there's no negative dimension, we will only consider h = 4
Solve for the base :
