The equation used to model the cost of the bracelet would be y = 6c + 12, in which c is the number of charms on the bracelet. This is because even with no charms (c = 0), the bracelet still costs 12, which is the constant.
To solve for how many charms you can get with $96, you can plug 96 in for y and solve.
y = 6c + 12
96 = 6c + 12
84 = 6c
14 = c