It's not about the answer I just want to understand all the steps

Let f(X) = 3 + DX and point P = |2.= a. Use the following definition of the slope of the tangent line at x = a to find the slope of the line tangent to the graph of fat P. f(a + h) - f(a) an = lim h-0 b. Determine an equation of the tangent line at P