Please help:

The total cost of gift baskets include the cost of each basket and a one time delivery fee. One company bought 40 baskets for a total of $715 and another company bought 400 baskets for $5,935. What is the cost per basket? What is the cost for the one-time delivery fee?

2 answers

If the fee is f and the cost of a basket is c, then

f+40c = 715
f+400c = 5935

Multiply the 1st equation by 10 so we can eliminate c:

10f + 400c = 7150
f + 400c = 5935

subtract and you have

9f = 1215
f = 135
How did you know to multiply by 10 to eliminate C?