1)(39+х)-84=78
39+x-84=78
x=78-39+84=123
==================================
2)(х-83)+316=425
x-83+316 = 425
x=425+83-316 =192
==================================
3)(600-х)-92=126
600-x - 92 = 126
-x = 126-600+92 =
-x = -382
x=382
====================================
х+27-14=36
x=36-27+14 = 23