Sara is 9 years less than twice Brenda's age. If Sara is 21, write an equation to find Brenda's age. (we don't want to find Brenda's age.. We just want to write the equation

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.)