Answer :
Let d stand for the cost of a drink and p stand for the cost of a box of popcorn.
d + p = 0.9
2d + p = 1.45
d + p = 0.9
d = 0.9 - p
2(0.9 - p) + p = 1.45
1.8 - 2p + p = 1.45
1.8 - p = 1.45
-p = -0.35
p = 0.35
A box of popcorn costs 35p.
d + p = 0.9
2d + p = 1.45
d + p = 0.9
d = 0.9 - p
2(0.9 - p) + p = 1.45
1.8 - 2p + p = 1.45
1.8 - p = 1.45
-p = -0.35
p = 0.35
A box of popcorn costs 35p.
