assuming the x means multiply
evaluate parenthsees fist
7x10=70
-7x?=-7?
7x9=63
so
63=70-7?
minus 70 both sides
-7=-7?
divide both sides by -7
1=?
an eaier way to do it is
regocnize we can undistribute the 7 because
ab-ac=a(b-c)
so
(7x10)-(7x?)=7(10-?)
now we got
7x9=7(10-?)
divide both sides by 7
9=10-?
minus 10
-1=-?
times -1
1=?
it is 1
