Differentiation mixed with Line Equation

the problems goes like this.

f(x) = x^5 + 5e^x , find f'(5)

So I did that and found f'(x) = 5x^4 + 5e^x. Finding f'(5) = 3867

Use this to find the equation of the tangent line to the curve y = x^5 + 5e^x at the point (a,f(a)) when a=5 . The equation of this tangent line can be written in the form y=mx+b where m is: 3867

I found out that part easily, by putting 5 into f'(x)

But the last part of the question is:

and where b is: ?

I have no idea. I tried putting 5 into y = mx+b and adding in the slope but that gives me .2 which is an incorrect answer. Been trying to figure this one out forever!

Please help!!

Thanks,

-MoMo