Searching for intermediate value

Let's say I have two columns of data like this:

x y
147 46.8
148 48.2
149 49.6
150 50.4
151 51.2
152 52.6

I want to find what x value corresponds to a value of y = 50. For example in this data, at y = 50, x =149.5. So essentially I have to search for an interpolated value that isn't actually in the data.

I've tried getting the equation of a line using SLOPE() and INTERCEPT() and then solving for x, but this has given me inaccurate results.

Thanks Andy. It works great, however some sections have data similar to this, but in descending order. Is there an easy way to sort the list in ascending order or use vlookup for a descending list?

I tried using that formula but it just returns the first value in the list. However it doesn't have those curly {} brackets around it. When I add those, Excel doesn't treat it as a formula. I have too many different columns to search in order to sort them all using the menu.