P = 28 cm
[tex] \frac{l}{L} = \frac{3}{4} [/tex]
[tex] \frac{l}{3} = \frac{L}{4} = k [/tex]
[tex] \frac{l}{3} = k[/tex]
l = 3k
[tex] \frac{L}{4} = k[/tex]
L = 4k
P = 2L + 2l = 2 · 4k + 2 · 3k = 8k + 6k = 14k
28 = 14k
k = 28 : 14
k = 2
L = 2 · 4 = 8 cm
l = 2 · 3 = 6 cm
A = L · l = 8 · 6 = 48 cm²