You could find his score for those three games by subtracting -700 and 400 to get 1100.
3x + (x+3) = 19
4x + 3 = 19
4x = 16
x = 4
y= x+3
y= 4+3
y= 7
we do 2x-1/y=w+2/2z
2x-1/y we multiple each side y
2x-1/y×y=2x-1
then w+2/2z
we said×2z×2z
then we got
w+2
later
2x-1=w+2=
then 1 become another side
which is 1+2=3
then
w=3-2x
I hope it's correct