Fraction help please

Question

Ammaar put 4/7 of the money he earned raking leaves in the bank. He spent 1/3 of all of his money on a book.

Part A

Drag and drop the fractions into the boxes to create an expression with common denominators that can be used to find the difference between the fraction of money Ammaar put in the bank and the fraction he spent on the book. Fractions may be used more than once or not at all. Drag and drop the fractions into the appropriate boxes.

1/10     4/10 7/10     8/10 1/21 4/21    7/21 12/21

Part B

What is the difference between the fraction of money Ammaar put in the bank and the fraction he spent on the book?

Answer 1

The LCD of 7 and 3 is 21.

4/7 = 12/21

1/3 = 7/21

4/7 - 1/3 = 12/21 - 7/21 = 5/21