A - 80 = 320 + 350
a - 80 = 670
a = 670 + 80
a = 750
750 - 80 = 320 + 350
670 = 670
===================
590 - x = 110 + 260
590 - x = 370
x = 590 - 370
x = 220
590 - 220 = 110 + 260
370 = 370
===================
x + 120 = 900 - 540
x + 120 = 360
x = 360 - 120
x = 240
240 + 120 = 900 - 540
360 = 360
===================
480 + b = 900 - 150
480 + b = 750
b = 750 - 480
b = 270
480 + 270 = 900 - 150
750 = 750