Answer:
top left=4, top right =9, bottom left=12, bottom right =8 -- set it up as a system of small equations.
Step-by-step explanation:
x+y=13
x+w=16
y+z=17
w-z=4
x=16-w
y=17-z
then substitute.
(16-w)+y=13
-w+y= -3
-w+(17-z)= -3
-w-z = -20 add that to w-z=4
-2z= -16
z=8
then plug back in until you have all 4 values
w-(8)=4 --> w=12
-(12)+y= -3 --> -12+y= -3 --> y=9
x+(9)=13 --> x=4
