The elimination method: to eliminate x, and than add the equations

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

Write the equation for the parabola that has x− intercepts (−2,0) and (4,0) and y− intercept (0,4).

Acollection of coins has value of 64 cents. there are two more nickels than dimes and three times as many pennies as dimes in this collection. how many of each kind of coin are in the collection?