Răspuns :
3400+(2500-x)=4428=>2500-x=4428-3400=>2500-x=1028=>x=2500-1028=>x=1472
3400+(2500-x)=4428
4428-3400=1028
2500-x=1028
x=2500-1028
x=1572
4428-3400=1028
2500-x=1028
x=2500-1028
x=1572