Answer :

TSO
31+34 = 90 -n
65 = 90 - n
65+n = 90
n= 90-65
n= 25

45+1 = 70-k
46 = 70-k
46+ k = 70
k = 70-46
k= 24

6x9 = 41+m
54 = 41+m
m = 54-41
m = 13

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