An object moves along the x - axis and its position is given by the function s(t)=t3−7t2+2t+5. find the acceleration at time t=−1.

Take first derivitive, remember dy/dx x^a=ax^(a-1)

first derivitive
s'(t)=3x^2-14t+2
2nd
s''t(t)=6x-14
s''(t)=a(t)=acceleration

at t=-1

a(-1)=6(-1)-14
a(-1)=-6-14
a(-1)=-20

acceleration is -20

(-1*3) - (7*-1*2)+(2*-1) + 5 = 14 
Hope this helps

All you have to do is multiply