6e^(2x+3)
= 6e^(2x+3)*2
=12e^(2x+3)
The derivative of e^x is e^x but you also have to multiply it by the derivative of the inside function (by the chain rule) which in this case is 2 since the derivative of 2x+3 is 2. The only variable in this equation is x. e is not a variable but a value equaling approx. 2.71828-you can check on your calculatro by doing e^(1)
I'm not sure if your teacher meant the simple formula f'(x) = nx^n-1(where n is the integer and x is the variable or the full
lim h goes to 0 of (f(a+h)-f(a))/h formula though