Question 831384
A shopkeeper buys a crate of eggs at $1.50 per dozen. he buys another crate, containing 3 dozen more than the first crate, at $2.00 per dozen. He sells them all for $2.50 a dozen and makes $15 profit. How many dozens were there in each of the crates?

let the eggs be x dozens  
cost of eggs = 1.5x

Crate II.
x+3 dozens
cost = 2*(x+3)

Cost of eggs = 1.5x+2(x+3)
= 1.5x+2x+6
=3.5x+6

Number of eggs = x+(x+3)

sold for 2.50

Sales = 2.50(2x+3)
=5x+7.5

Sales - cost = 15

2.50(2x+3)-1.5x+2(x+3)=15

5x+7.50-3.5x-6=15

1.5x=13.5
x=9

Crate I--- 9 dozens
Crate II---- 12 dozens