5. A mass weighing 16 pounds stretches a spring 3 inches. The medium offers a damping force that is numerically equal to 2 times the instantaneous velocity. The mass is released from equilibrium with a downward velocity of 3 inches per second. a. Determine the equation of motion. b. Determine the first time (after t = 0) when the mass first passes through equilibrium. 6. Solve the IVP. y" -8y +15y9te² = y(0) = -1, y'(0) = 3 7. Find the general solution of the ODE. x²y"-2y=3x² - 1 x > 0 8. Find the general solution of the ODE. y"+2y24y=12x+9-e4x 9. Solve the IVP. y"" +12y" +36y' = 0 y(0) = 0, y'(0) = 1, y"(0) = = -7 1