Answer:
y = (x^2 + 6) / 2
Explanation:
Original function:

To find the inverse of a function we have to switch the x and y values and solve for y again
x = sqrt (2y-6)
To get rid of a square root we square the square root so:
x^2 = 2y-6
Add 6
x^2 + 6 = 2y
Divide by 2
y = (x^2 + 6) / 2