1) 8
reason: radius is diameter divided by two, 16/2
2) 6
reason: diameter is radius times two, 3 × 2
3) 87.92
reason: circumfrence is pi times diameter, 28 × 3.14
4) 31.4
reason: circumfrence is pi times diameter, 10 × 3.14
6) 61.12
reason: 10 + 10 +8+8= 36 8×3.14= 25.12 36 + 25.12= 61.12
7) 69.0172
reason: 7^2× 3.14= 69.0172
8) 346.185
reason: 21÷2= 10.5 3.14×10.5^2= 69.0172