Hi all, I am new to this site and I'm just starting to get back into education. I need to figure out acceleration from speed then transpose for t to find out when accel reaches 0.

I'm given the formula for speed

v=12te^{-(t/2) }+5

so my acceleration, a= dv/dt = -6te^{^-(0.5t)}- 6e^{-(0.5t}^{)}which after 4.5s a= -3.48 m/s^{2}

if this is correct so far, I have no idea. If by some miracle it is, I need to transpose for t, to find the time when acceleration reaches zero. Any help would be greatly appreciated.

steve