Graph the curve and find its exact length

1) y = (x^2)/2 - (lnx)/4, 2<x<4

How do I find this arc length when I am not given an x = function?

2) A steady wind blows a kite due west. The kite's height above ground from horizontal position x = 0 to x = 80 ft is given by y = 150 - (1/40)(x-50)^2. Find the distance traveled by the kite.

Am I supposed to integrate the y function from 0 to 80? If so, what do i do for the x function?

thanks for any help.