You've got to learn how to do mental math or visualize a number line and do it. Didn't you learn subtraction in grade school?
It is 50% because 18 divided by nine is two. 100 divided by 2 in 50.
8)p-4= -9+p
+4 +4
p= -3 +p
p = 3p
p= 3
10) 12= -4(-6x-3)
12= (24x) - (-12)
+12 +12
24= 24x
x=1
12) -(7-4x)=9
-1 (7-4x)=9
(-7) - (-4x)=9
+7 +7
-4x=16
x =-4