Step-by-step explanation:
by using similarity and enlargement
10/8 = 7+y/7
70=56+8y
8y=14
y= 7/4
10/8 = 5+x/5
50=40+8x
x = 8/10 = 4/5
If one book = 1/8, then you can just multiply it by 3, for the three mystery books. 8x3= 24, so tony has 24 books in all.
Answer: 51
80+49=129
180-129= 51