(a) To find 45% of 60, you can multiply 60 by 0.45:
\[ 45% \text{ of } 60 = 60 \times 0.45 = 27 \]
So, 45% of 60 is 27.
(b) To find what percent of 72 is 18, you can use the formula:
\[ \text{Percent} = \left(\frac{\text{Part}}{\text{Whole}}\right) \times 100 \]
Where the part is 18 and the whole is 72:
\[ \text{Percent} = \left(\frac{18}{72}\right) \times 100 = 0.25 \times 100 = 25% \]
So, 18 is 25% of 72.