Question 44977
You should notice that {{{s-st=s(1-t)}}}.
I understand how you would not notice that at first, but after you have been shown it once you will find it hard to forget. The more practice you have with this sort of thing, the more obvious it becomes.
Here's the solution:
{{{s-st=p}}}
{{{s(1-t)=p}}}
{{{s=p/(1-t)}}}
I hope this helps.
P.S. I am trying to start up my own homework help website. I would be extremely grateful if you would e-mail me some feedback on the help you received to adam.chapman@student.manchester.ac.uk
Adam