Unfortunately, you can't.http://www.elevenplusexams.co.uk/advice/standardised-scores-an-explanation
This link explains how it works generally. Specifically for Sale each of the 3 papers count for a third of the marks. Each paper's raw score is standardised to give a mark out of 141, so the maximum mark you can get is 423 (i.e. 3 x 141). In order to get a pass mark of 353 this means that on average you need to be aiming for 118/119 in each paper. However, what that standardised score equates to in terms of raw scores is anyone's guess. As a rule of thumb I would say that if you are getting over 80% in the GL papers then you are in the right area, although the higher the better for comfort. Plus, you don't need to get 118 in each paper. A lower score can be offset by 2 higher scores in the other two papers.