tolong jawaban no 19 pakai cara jangan abal abalan

diketahui : luas lingkarang = 616 cm2
phi = 22/7
ditanya : keliling lingkaran ?
jawab: luas lingkaran = 616 cm2
phi × r2 = 616 cm2
22/7 × r2 = 616 cm2
r2 = 616/22/7
r2 = 616 × 7/22
r2 = 196
r = akar 196
r = 14
keliling lingkaran = 2 × phi × r
= 2 × 22/7 × 14
= 88 cm