If a rock is thrown upward on the planet Mars with a velocity of 10 m/s, its height (in meters) after t seconds is given by H=10t-1.86t^2.
(a) Find the velocity of the rock after one second.
(b) Find the velocity of the rock when t=a.
there happens to be a lot of people on this website who know how to find the derivative of that. it could also be that you do not know how to approach the problem as opposed to knowing how to approach the problem but not being able to do it.
use the power rule $\displaystyle \frac d{dx} x^n = nx^{n - 1}$. n is a constant here. and note that the derivative of a constant times a function is just the constant times the derivative of the function. (here you use t as the variable instead of x, of course).
and try in the future not to bite the hand that feeds you. it's silly to use that tone with someone who is trying to help you