A motionless light vertical hanging spring, stiness constant has a relaxed length, $.$ A mass, is attached to the end of the

spring and comes to equilibrium. With the mass and spring at rest, you very slowly pull down on the mass so that the spring

stretches an additional length, $.$ At that point, you give the mass an upward initial speed, $.$

Which of the following equations will you need to solve to determine the speed, of the mass when it passes through the

equilibrium position of the spring $?$