Step-by-step explanation:
h=b-4
A=30ft^2
A=1/2bh
30=1/2b(b-h)
Cross Multiply
60=b(b-4)
60=b^2-4b
b^2-4b-60=0
Factorise the equation
(b^2+6) (-10b-60)
b(b+6)-10(b+6)
(b-10) (b+6)
b-10=0 or b+6=0
b=10 or b=-6
base =10 (since measurement can not be negative)
h=b-4
Sub the value of b
h = 10-4
h=6
So the height is 6ft and base is 10ft
