We have been given 2 instances with 2 unknowns. We can build a system of simultaneous equations.
x - price of a jacket
y - price of pair of sweatpants
when he buys 15 jackets - price - 15x
and 12 pairs of sweatpants - price - 12y
total price he paid was 348
first equation,
15x + 12y = 348
next he buys 8 jackets - 8x
and 8 pairs of sweatpants - 8y
Total price - 200
second equation
8x + 8y = 200
system of equations therefore,
15x + 12y = 348
8x + 8y = 200