1/2: x::1:8

1x =1/2 of 8

x = 4

Hello Alice,

Can you first read the topic Sticky: How to: technical and scientific documentation/formulas - LINK, so that you can put the question clearly on this board?
Formulating the question properly is essential in math questions!

I see that you received an answer, but the intention of this board is to EXPLAIN you how to solve your problem, for which we need to see the proper question first, and the way you approached that question yourself.

Was your intention to show a string? (Like 1/2 : x : : 1 : 8) Than something seems missing between x and 1 !
Or perhaps 2 ratios? (Like 1/2 : x and 1 : 8) In that case ratio 1/2 : x and ratio 1 : 8) are related. You know from the second term that the factor is 8, so it is easy to calculate x from 1/2 also (with that same factor).