Question 638022
The missing leg is sqrt(12^2 - 9^2) = sqrt(144-81) = sqrt(63) = 3*sqrt(7), which is the base.


So the exact area is


A = (b*h)/2


A = (3*sqrt(7)*9)/2


A = (27*sqrt(7))/2


which approximates to 


A = 35.717642699 square yards.