If the base of the isosceles triangle lies on the x axis and one of the base angles is located on the origin, then the third vertex would lie somewhere in Quadrant I. If the coordinate of the second base angle is (2a, 0), then the coordinates that should be assigned to the third vertex of the isosceles triangle is (a, b).
L+S=8, L=8-S
500L+200S=2200, using L from above in this equation gives you:
500(8-S)+200S=2200
4000-500S+200S=2200
4000-300S=2200
-300S=-1800
S=6, and since L=8-S:
L=2
So Rita bought 2 large packets and 6 small packets.