Solution:
Let "x" be the number of hot dogs sold
Let "y" be the number of sodas sold
Each hot dog costs $1.50 and each soda costs $0.50
You sold a total of 87 hot dogs and sodas combined
Therefore,
x + y = 87
y = 87 - x -------- eqn 1
At the end of the night you made a total of $78.50
Therefore,
1.50x + 0.50y = 78.50 ------ eqn 2
Substitute eqn 1 in eqn 2
1.5x + 0.5(87 - x) = 78.5
1.5x + 43.5 - 0.5x = 78.5
x = 78.5 - 43.5
x = 35
Substitute x = 35 in eqn 1
y = 87 - 35
y = 52
Thus 35 hot dogs and 52 sodas were sold