True or false, when n is an negative integer, n-n=0

Agrocery store has 12 lb of trail mix that is 10% banana chips. the store's manager would like to add banana chips to bring the new mix up to 25% banana chips. write and solve a system of equations to find out how many pounds of banana chips manager needs to add.

Which of the following answers is 7/9 simplified? 7/9 2/9 11/9 2/7

Asphere has a diameter of 10 in. what is the volume of the sphere?