To find the maximum number of donuts Leslie can buy, we need to divide the total amount of money she has by the cost of each donut.
First, we need to convert Leslie's dollars to cents, since the cost of each donut is given in cents. We can do this by multiplying the dollars by 100:
$20 * 100 = 2000 cents
Now we can divide the total amount of money (in cents) by the cost of each donut (85 cents) to find the maximum number of donuts Leslie can buy:
2000 cents ÷ 85 cents/donut ≈ 23.53 donuts
Since Leslie cannot buy a fraction of a donut, we will round down to the nearest whole number. Therefore, the maximum number of donuts Leslie can buy with $20 and with each donut costing 85 cents is 23 donuts.