1) (39+x )-84=78
39+x=78+84
39+x=162
x=123
(38+123)-84=78
2) (x-83)+316=425
x-83=109
x=192
(192-83)+316=425
3)(600-x)-92=126
600-x=218
x=382
(600-382)-92=126
4)253-(x-459)=138
253-x+459=138
253-x=-321
x=253-(-321)
x=574
253-(574-459)=138
5)502-(217-x)=421
502-217+x=421
-217+x=-81
x=136
502-(217-136)=421
6)871-(x+157)=385
871-x-157=385
871-x=542
x=329
871-(329+157)=385