a)25+a:(20+112-4)=39
25+a:128=39
25+a=39×128
25+a= 4992
a=4992-25
a=4967
b)52×5+b=124×3+25×4
260+b=372+100
260+b=472
b=472-260
b=212
c)20+3×12+c=148
20+36+c=148
56+c=148
c=148-56
c=92
d)d-2×(480×2-90:10)+5=75
d-2×(960-9)+5=75
d-2×951+5=75
d-1902+5=75
d-1902=75-5
d-1902=70
d=70+1902
d=1972
