The procedure is as follows: 1. Take the derivative of s by t. You will get a quadratic polynomial of t for the velocity, v(t) =. 2. Solve the quadratic equation v(t) = -2 to find the time moment when the velocity is - 2 . 3. Take the second derivative of s by t to get the expression for the acceleration a(t). 4. Substitute the found value of t into the expression for acceleration to determine the unknown acceleration. Good luck!