First Derivative? 1st physics calculus class-help

[NanoTech]

the position of a particle on the x-axis is given:
x = 7.8 + 9.2t -2.1t^3

what is the velocity at t = 3.5 s ?

so i need to find the derivative of d/dt (7.8 + 9.2t -2.1t^3)

i'm completely lost on how to find it. thanks.

[himanshu121]

Look up at the formula its simple plug in pro

d/dt(constatnt)=0
and
\frac{dx^n}{dt}=nx^{n-1}\frac{dx}{dt}

[NanoTech]

Thanks. That was really easy now that I see the correct formula. Differentiation by exponent.