Tolong bantuannya no 3 & 4

3. a.) K = 4s
84 = (4x + 5)
84 : 4x = 5
21x = 5
4,5 = x
b.) (4x+5) = (4x4,5+5)
= 23 cm
c.) L = sxs
= 23x23
= 529 cm2