Answer
It is a better idea to solve for $c$ using $a$, as the rounding error would be reduced.
Work Step by Step
As shown in Example 1, while angle $\angle B$ has already been given, side $b$ has to be obtained using law of cosines; and the result obtained must be approximated.
Therefore, if we solve for $c$ using $b$, we would come up with a result that needs to be approximated one more time, meaning the rounding error would be quite significant.
Instead, if we solve for $c$ using $a$, an already given value, we would only need to approximate the result one time, so the rounding error would be reduced compared with when we use $b$.
Therefore, it is a better idea to solve for $c$ using $a$, as the rounding error would be reduced.
