The reduction ratio is 0.875 to 7 / 8, and 7 / 20 to 0.25
875:7 / 8 = 1:1
25 = 7:5
Simple operation of 1 / 7 * 20 + 4 / 7 * 16
1 / 7 * 20 + 4 / 7 * 16
=1 / 7 * (20 + 4 * 16)
=1 / 7 * 84
=12
Simple calculation of 1 / 7 × 20 + 4 / 7 × 16
1/7×20+4/7×16
=1/7x20+1/7x64
=1/7x(20+64)
=1/7x84
=12