Answer and explain ILL MARK BRAINLIEST

If a + b = 28 and a - b = 10, then b =?

Mary and roberto bought identical backpacks at different stores. mary's backpack originally cost $65 and was discounted 25%. roberto's backpack originally cost $75 and was on sale for 30% off on the original price. which backpack was the better buy?

Write the expression 7x^3-28xy^2 as the product of 3 factors