BC is the height of triangle BCD
So
80 = (1/2) CD * BC
160 = 15 * BC
160 / 15 = BC = 32/3
And ABCD is a trapezoid...so its area =
(1/2) BC * ( AB + CD) =
(1/2) (32/3) ( 9 + 15) =
(1/2) ( 32/3) (24) =
128
So....area of triangle BAD = [ABCD ] - [ BCD ] = 128 - 80 = 48
