Question

（X×N＋ 8）÷N＝90 （X×N－12）÷N＝85

Answer 1

（X×N＋ 8）÷N＝90

X×N＋ 8＝90×N

X×N = 90×N-8

（X×N－12）÷N＝85

X×N－12＝85×N

X×N =85×N+12

所以90×N-8=85×N+12

N=4

X=88