A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
I know this comes extremely late... As I just encountered this issue for the first time... Hope this can save some time for others in the future.
For anyone having this issue, on your Visual Basic Editor, there is a
Add Reference button on the lower left corner. Open it up, tick
Solver, press OK, then it should work.
I think the reason why this becomes such a confusing topic, is because Excel has changed its UI in 2016, and suddenly Add Reference cannot be found using previous tutorials you could find online.