Answer:

Step-by-step explanation:
We require more information by I will explain in principle:
If Type A has at least 300 hours and Type B at least 400 hours.

You need to determine the Probability density function of X and Y and then subtract 1 from both

This will give you the probability of the expression.
2 4/5, that is it in simplest form
3/6 and 4/8... is equivalent also to 1/2... If that's what you are looking for...
248 is your answer I am thankful I can help you let me know if you need anything else