Find and simplify an expression for a . b in terms of t. hence or otherwise, find the values of t for which the angle between a and b is obtus

What is the greatest common factor of 8 and 36

Having a hard time understanding this question (see attachment).

Fatima plans to spend at least $15 and at most $20 dollars on sketch pads and pencils. if she buys 2 sketchpads, how many pemcils can she buy while staying in her price range? fatima can buy between and pencils. ? (type whole numbers. use ascending? order.)