（5.3×3.75+3.75×3.5）÷2.2
=3.75x(5.3+3.5）÷2.2
= 3.75x8.8÷2.2
=3.75x4
=（3又3/4）x4
=15
9.6÷（4.8×7.2+2.8×4.8）
=9.6÷4.8×（7.2+2.8）
=2×10
=20