which number should replace the question mark?

问题描述:

which number should replace the question mark?
72 64 17
59 48 29
61 53 71
26 17

是18
中间一个数等于每一行第一个数减去最后一个数的个位和十位之和.
64=72-(1+7)
48=59-(2+9)
53=61-(7+1)
所以 =26-(1+7)=18