If 5x2 + y4 = -9 then evaluate the second derivative of y with respect to x when x = 2 and y = 1

Amuffin recipe, which yields 12 muffins, calls for cup of milk for every 1 cups of flour. the same recipe calls for cup of coconut for every cup of chopped apple. to yield a batch of 30 muffins, how much flour will be needed in the mix?

How is working backward similar to solving an equation?

If the sales price of a dvd is $20 and the markup is 34%, what is the cost of the dvd?