Question

Find the unknown length for the triangle

Answer 1

Area for a triangle = (b*h)/2
h=12, b is unknown
so b*12/2=18(your total area)

12b/2=18 (times by 2 to isolate b)

12b=36 (divide by 12 to isolate b)

unknown length b=3

Answer 2

Unknown length = 18/12 = 1.5

answer
A.  1.5 ft