When are the sum, difference, product and quotient of two monomials also a monomial? PLEASE HELP I WILL GIVE BRAINLIEST!

If f(x)=-x^2+6x-1 and g(x)=3x^2-4x-1,find(f+g)(x)

Suzanne began a trip with 18 1/2 gallons of gas in the gas tank of her car if she hughes 17 3/4 gallons on the trip how many gallons does she have left once she finish the trip

Write the equation in logarithmic form 8^x=64