Need help with these few problems where it's using the definition of a derivative method

(1) Use the definition of the derivative to calculate f'(8) where f(xx) = x + 3. (2) Use the definition of the derivative to calculate f'(2) where f(x) = Vx + 2. (3) Use the definition of the derivative to calculate f'(a) where f(x) = -3. (4) Use the definition of the derivative to find f'(t) where f(t) = (t2 -3). 2+