7)
7b + 6b - 29 = 374
13b = 374 + 29
13b = 403
b = 403 : 13
b = 31
------------------------------------
7 * 31 + 6 * 31 - 29 = 374
217 + 186 - 29 = 374
403 - 29 = 374
374 = 374
8)
19y - 12y - 47 = 1388
7y = 1388 + 47
7y = 1435
y = 1435 : 7
y = 205
--------------------------------------------
19 * 205 - 12 * 205 - 47 = 1388
3895 - 2460 - 47 = 1388
1388 = 1388