I'm having trouble with this problem

In an engine, a piston oscillates with simple harmonic motion so that its position varies according to the expression, X = 8.00 cos 5t + 6 where x is in centimeters and t is in seconds. (a) At t = 0, find the position of the piston. 0 X This would be correct if the phase constant were 7/2. cm (b) At t = 0, find velocity of the piston. cm/s (c) At t = 0, find acceleration of the piston. cm/s2 (d) Find the period and amplitude of the motion. period S amplitude cm