Your question is unclear. You want to find x and d in a sequence.
3 successive terms of a arithmetic sequence would be x, x+d and x+2d
which means3x+3d=15, i.e. x+d=5
The product of those terms is x3+3dx2+2d2x=1.05 is not so easy to solve.
Is this what you really meant?
And then what is it you really want to find.