Paul is spreading grass seed on an area of his lawn that is 9 feet wide and 10 feet long. A bag of grass seed covers 15 square feet. How many bags of see will paul need to cover the area? What is the hidden questions? What is the answer to the hidden question? Why do you need this answer to solve the problem?

Area of the field should be 9*10 = 90 square feet.

a bag of grass seeds cover 15 square feet.

so if you need to know how many bags should be used, then,

Total area of field / area covered by 1 bag of grass seeds.

= 90/15 = 6 bags

he needs to use 6 bags of grass seeds to cover the whole field.

I don't think there are any 'hidden' questions, though you can consider the 2nd part of the question I guess. (how many bags of seed will Paul ...)