Help with homework assignment in math 213

Complete the Brain Teaser (Figure 4-17) from our text book Problem Solving Approach to Mathematics for Elementary School Teachers Chapter 4.

Brain Teaser:

For any n x m rectangle such that GCD(n,m)=1, find a rule for determining the number of unit squares (1 x 1)

that a diagonal passes through.  For example, in the drawings in Figure 4-17, the diagonal passes through

8 and 6 unit squares, respectively.

Prepare a 350 to 700 word summary of your Teams findings to explain the rationale of your rule.

can anyone help me with this, if so please let me know what else you need if anything.