Pardon the handwriting

This uses a bit of the use models and a bit of algebra. If you can understand this then youre doing good.

All four people are denoted by the letters. So first off focus on the amount spent by all 4 people, which is 1000-200= $800

This is for all 4 people. At the same time, A and W together spent $20 less than S and J combined. This is how i get both the equations:
A+W+S+J=$800
A+W+20=S+J

Now you want to remove as many letters as possible. It is recommended to keep A and W, as there is a value for W. Therefore, we can try to remove the letters S+J.

You can do this by adding both equations together, right hand side + right hand side = left hand side + left hand side. This allows you to cancel out S+J, and that is how i got A+W=$390

We know W=90, and A is 5 times of S. You can slowly solve each of the letters like the bottom right of thr picture, and hence you can find A+J.

You can try and test the values of each letters to see if they are correct. Go try it out. Hope it helped!