let

a = the length of the base of the triangle, a>0

h = the height of the triangle, h>0

A = 16 ft^2 is the area of the triangle

the base of the triangle is 4 feet less than 3 times the height:

a = 3h - 4

the area is 16 square feet:

(1/2)ah = 16

plug a = 3h - 4 into the last equations:

(1/2)(3h - 4)h = 16

by solving we find:

h = 4 ft

click here to see the step by step solution of the equation:

a = 3*4 - 4 = 8 ft

the dimensions of the triangle are: the base is 8 ft and the height is 4 ft.