Adding which terms to 3x^2y would result in a monomial?

The area of a rectangle is 15+5y square feet. which of the following expressions could be the length of the sides of the rectangle, in feet a. 5 and 3y b. 5 and 3+y c. 5 and 5+y d. 3 and 5+3y

The sum of two numbers is 12 and their difference is 18 what are the two numbers

The standard deviation for a set of data is 5.5. the mean is 265. what is the margin of error?