The first thing we want to do is define our variables. We want to take the information we have and define it in useful terms. We can relate all of the information back to a penny.
Let P = number of pennies, N the number of nickels and D the number of dimes, then
N = P - 7, and
D = N + 4
=(P - 7) + 4
= P - 3
We must now use the next set of information given. The total is $3.35 or 335 cents. We know that the number of pennies, plus 5 cents times the number of nickels, plus 10 cents times the number of dimes will be equal to 335
P + 5N + 10D = 335
Now we we can plug in what we defined earlier and solve for P.
Once you have found P, N and D make sure that you check that there are four more dimes than nickels, seven fewer nickels than pennies and the total value is $3.35