c : Grundseite
h = c - 4 => c = h + 4
A = c * h / 2
A = ( h + 4 ) * h / 2 = 48
h^2 / 2 + 4 * h / 2 = 48
h^2 / 2 + 2 * h = 48 | * 2
h^2 + 4 * h = 96
h^2 + 4 * h + 2^2 = 96 + 2^2
( h + 2 )^2 = 100
h + 2 = 10
h = 8
c = h + 4
c = 12
A = 12 * 8 / 2 = 48 | stimmt