rumus mencari atas trapesium jika luasnya sudah diketahui

Rumus luas trapesium =1/2×(a+b)×t
Misalkan luas trapesium = 32cm2
b = 5cm,t = 8cm
Maka atas trapesium=
L trapesium = 1/2×(a+5cm)×8cm
32cm2 = 1/2×(a+5cm)×8cm
32cm2×2/1 = 8cm a+40cm2
64cm2 = 8cm a+40cm2
64cm2-40cm2 = 8cm a
8cm a = 24cm2
a =24cm2/8cm
a =3cm