The average of the first 18 positive multiples of 7 is:

To find the average of the first 18 positive multiples of 7, we can use the properties of arithmetic progressions.

The first 18 positive multiples of 7 are:
7, 14, 21, ..., 7 * 18

This sequence forms an arithmetic progression (AP) where:
- The first term (a) is 7.
- The last term (l) is 7 * 18 = 126.
- The total number of terms (n) is 18.

The average (arithmetic mean) of an arithmetic progression can be calculated using the formula:
$\text{Average}=\frac{a+l}{2}$

Substituting the values of the first term and the last term into the formula:
$\text{Average}=\frac{7+126}{2}$

Simplifying the numerator:
$\text{Average}=\frac{133}{2}$

Dividing 133 by 2 yields:
$\text{Average}=66.5$

Therefore, the correct option is 66.5.