a) a:b=5 rest 4 => a=5b+4
a+b=34 => 5b+4+b=34 => 6b=34-4 => 6b=30 => b=30:6 => b=5
b) a:b=10 rest 3 => a=10b+3
a+b=69 => 10b+3+b=69 => 11b=69-3 => 11b=66 => b=66:11 => b=6
c) a:b=15 rest 6 => a=15b+6
a-b=286 => 15b+6-b=286 => 14b+6=286 => 14b=286-6 => 14b=280 => b=280:14 => b=20
d) a:b=12 rest 10 => a=12b+10
a-b=131 => 12b+10-b=131 => 11b+10=131 => 11b=131-10 => 11b=121 => b=121:11 => b=11