Let the number of cards equal x.
Set up an equation for both companies, set equal to each other and solve for x.
0.10x + 12 = 0.12x + 10
Subtractb0.10x from both sides:
12 = 0.02x + 10
Subtract 10 from both sides:
2 = 0.02x
Divide both sides by 0.02:
X = 2/0.02
X = 100
100 cards would be the same price for both companies.