But that is sort of the point. In theory, it's the same. But that's not how you should actually compute it.

The cheap way is to compute 21/7.

The hard way is to compute 1/7 (one floating point operation), and then multiply it by 21 (another floating point operation).

With matrices, the discrepancy in work and possibly precision between "solve Ax=b" and "compute x = A^-1 b" can be very large.