luas bangun datar yg diarsir adalah

L = 30x8= 240 cm²
L= axt/2 = 30x8 /2 = 120 cm²
L = 240 -120 = 120 cm²

a = 15 cm
t = 8 cm
2 ( LΔ ) = 2 ( [tex] \frac{1}{2} [/tex] . a . t ) =
2 ( [tex] \frac{1}{2} [/tex] . 15 . 8 ) = 
2 ( 15 . 4) = 
2 ( 60 ) = 120 cm