It doesn't look possible the way you've presented it

you could have that part of E is 15% of A and so E would be something like

.15A + .25B + .35C + .25D

and that's easy enough to put in a spreadsheet

have A1,,,D1 be the entries you know

and in E1 type =.15*A1 + .25*B1 + .35*C1 + .25*D1

but I really don't think thats the way you're supposed to go about it

it sounds more like you should have that E*.25 = B and also E*.25 = D which is a contradiction