Question 177611
*[tex \huge 12AB + 7B = 5A]


Add -5A to both sides, then add -7B to both sides:


*[tex \huge 12AB - 5A = -7B]


Factor out the A on the left:


*[tex \huge (12B - 5)A = -7B]


Multiply both sides by -1: (verification of the fact that (-1)(a - b) = (b - a) is left as an exercise for the student.)


*[tex \huge (5 - 12B)A = 7B]


Divide both side by (5 - 12B):


*[tex \huge A = \frac {7B}{5 - 12B}]