Carmen spent a total of $19.50 at a concession stand on snacks for herself and her friends hamburgers cost $3.50 and hotdogs cost 225 if you bought a total of seven snacks how many hotdogs did she buy

Hb=3.5, hd=2.25, hb+hd=7,

From the third, we can say hb=7-hd and we are told that:

3.5hb+2.25hd=19.5 using hb found above in this equation gives you:

3.5 (7-hd) + 2.25hd=19.5

24.5-3.5hd+2.25hd=19.5

-1.25hd=-5

hd=4

Carmen bought 4 hotdogs.