81, 6, 7, 1, 42
Mode ??
Median ??

No mode

Median 7

Step-by-step explanation:

Mode: The mode is the element that occurs most in the data set. In this case, all elements occur only once, so there is no mode.

Median: Arrange the data in an ascending order and the median is the middle value. If the number of values is an even number, the median will be the average of the two middle numbers.

Jane was charged $15/4 = $3.75 per item and George was charged
$39/12 = $3.25 per item, so in addition to the charge per item, there must be an extra charge for each purchase.

We note that George bought 12-4 = 8 more items than Jane and was charged
$39 - $15 = $24 more, or $24/8 = $3 more for each additional item. So if we figure $3 per item, we can find out that extra charge.

Jane paid 4 * $3 = $12 for her 4 items, plus $3 to make her total $15.
George paid 12 * $3 = $36 for his 12 items, plus $3 to make his total $39.
So we can see that if x is the number of items, the store charges
x times $3 plus an extra $3.

Using function notation, we write
f(x) = 3x + 3
and then work out the charge for 22 items:
f(22) = 3 * 22 + 3 = 66 + 3 = 69