pq + 12 = 3p + pr
Subtract pr from both sides
pq - pr + 12 = 3p
Factor the p from the first two terms on the left-hand side
p(q-r) + 12 = 3p
Use the fact that q - r = 7
7p + 12 = 3p
Subtract 3p from both sides
4p + 12 = 0
Subtract 12 from both sides
4p = -12
Divide both sides by 4
p = -3
.
pq + 12 = 3p + pr
Subtract pr from both sides
pq - pr + 12 = 3p
Factor the p from the first two terms on the left-hand side
p(q-r) + 12 = 3p
Use the fact that q - r = 7
7p + 12 = 3p
Subtract 3p from both sides
4p + 12 = 0
Subtract 12 from both sides
4p = -12
Divide both sides by 4
p = -3
.