13: b=145 (180-35)
14: b=61 (90-29)
15: b=43 (243+94=337 , 380-337=43)
16: b=131 (180-49)
17: b=90
18: b=73
19: x=23 (3x+18+93=180 , 3x+111=180 , 3x=69 , x=23)
20: x=79 (296+29=325 , 380-325=55 , x-24=55 , 55+24=79)
21: x=20 (2+3x=62 , 62-2=60 , 3x=60 , x=20)
22: x=8 (6x+2+40=90 , 90-42=48 , 6x=48 , x=8)
