tolong jawab soal ini dong

( A ) a + 3a = 28
4a = 28
a= 7
a = 7 ----->jari" (1)
3a = 21----->jari" (2)

anggap aja phi ( ^ ) dan pangkat ( @ ) ( B ) L1 : L2
= ^ x r@2 : ^ x r@2
=7@2 : 21@2
=49 : 441
=1 : 9

( C ) L1 = 22/7 x 7@2
= 154
L2 = 22/7 x 21@2
= 1386
selisih luas = L2 - L1
= 1386 - 154
= 1232
K1 =22/7 x 14
= 44
K2 = 22/7 x 42
= 132
selisih keliling = K2 - K1
= 132 - 44
= 88