4. A. X:17=9 r 15 => x = 9*17+15 =>x=153+15=>x=168.
B. X:25=11 r 13 =>x=11*25+13=>x=275+13=>x=288
C. X:18=12 r5=> x=18*12+5=>x=216+5=>x=221
D. X:37=8 r 9 => x=37*8+9=>x=296+9=>x=305.
E. X:13=12 r 4=> x=13*12+4=>x=156+4=>x=160.
5. A. a+b=45
a:b=4 r 5/*b=>a=4b+5
a+b=45=>4b+5+b=45/-5=>4b + b=40=>5b=40/:5=>b=8
a=4b+5=>a=4*8+5=>a=32+5=>a=37
B. a-b=158
a:b=18 r 5/*b =>a=18b+5
a-b=158=> 18b+5 - b=158/-5 => 18b-b =153=>17b=153/:17=>b=9
a=18b+5=>a=18*9+5=>a=162+5=>a=167