Visualize a number line. Move your point $6$ spaces to the right, and then $18$ spaces to the left. Where is your point now located?

$-12$

Find the difference between $25$ and $12\frac{1}{2}$. The sign (positive or negative) of the solution is that of the larger number.

$-12\frac{1}{2}$

Since both numbers have the same sign, add them together. The solution will have that sign (positive or negative).

See part (a) or (b).