tolong nomer 26, pake cara ya..

2 × 3/4πr² + r² = 320
2 × 3/4.22/7.r² + r² = 320
2 × 66/28r² + r² = 320
2 × 33/14r² + r² = 320
66/14r² + r² = 320
33/7r² + 7/7r² = 320
40/7r² = 320
r² = 320/40/7
r² = 320 × 7/40
r² = 56cm²