Tolong ya pakai cara juga ok

1. luas = 78,5
1/4 × 3,14 × d^2 = 78,5
0,785 d^2 = 78,5
d^2 = 78,5 ÷ 0,785 = 100
d = √100 = 10

2) luas juring =168/360 × 3,14 × 7,5 × 7,5 = 82,425