Probability Trees - See linked image
A good visual method for this is a probability tree.
Each set of branches represents the probabilities of on coin being removed, the second set is out of 9 as the first coin is taken and not replaced.
Multiply along the lines to work out the probability of each of the combinations.
*Even though only 'Dime Dime' is needed, it is best to do all of them as this way you are able to get all marks in an exam; you can also add up all the final values as a check to see if you are right.
The number (variable n) would be 7. work is in the pic
800÷12=66.6666666667
hope it helps!
btw that my actual answer. it really long.
the cost to pick 3 pecks of peaches will be 14.75$