Правильное условие в приложении.
(39 + х) - 84 = 78
39 + х = 78 + 84
39 + х = 162
х = 162 - 39
х = 123
(39 + 123) - 84 = 78
162 - 84 = 78
78 = 78
(х - 83) + 316 = 425
х - 83 = 425 - 316
х - 83 = 109
х = 109 + 83
х = 192
(192 - 83) + 316 = 425
109 + 316 = 425
425 = 425
(600 - х) - 92 = 126
600 - х = 126 + 92
600 - х = 218
х = 600 - 218
х = 382
(600 - 382) - 92 = 126
218 - 92 = 126
126 = 126
253 - (х - 459) = 138
х - 459 = 253 - 138
х - 459 = 115
х = 115 + 459
х = 574
253 - (574 - 459) = 138
253 - 115 = 138
138 = 138
502 - (217 - х) = 421
217 - х = 502 - 421
217 - х = 81
х = 217 - 81
х = 136
502 - (217 - 136) = 421
502 - 81 = 421
421 = 421
871 - (х + 157) = 385
х + 157 = 871 - 385
х + 157 = 486
х = 486 - 157
х = 329
871 - (329 + 157) = 385
871 - 486 = 385
385 = 385
42:7=6
6*3=18
24:3=8
9*3=27
18+2=20+8=28-7=21+27=48