Dengan cara caranya , mohon bantuannya

L juring = alpha/360°×L lingkaran
L juring = 90°/360°×πr²
L juring = 1/4×3,14×10×10
L juring = 78,5 cm²
L∆ = ½×a×t
L∆ = ½×10×10
L∆ = 50 cm²
L tembereng = L juring - L∆
L tembereng = 78,5-50
L tembereng = 28,5 cm²