SOLUTION
Step 1: Assume that there is the same work to be done.
Let t be the time it will take both of them to finish the work.
Then Heather can do

while Perry can do

Step 2: Assume that both of them worked together, then we have that :

Step 3: We want to find the time it will take both of them to work together to finish the same job.

CONCLUSION: It will take
