Pre-Cal/Matrices/System of Equations

A bank teller is counting the total amount of money in a cash register at the end of the day. There is a total of $2600 in denominations of $1, $5, $10 and $20 dollar bills.

The total number of paper bills is $235. The number of twenty dollar bills is twice the number of $1 dollar bills and the number of $5 dollar bills is ten more than the number of $1 dollar bills. What is the system of equations to repersent the situation. Then use matrices to find the number of bills for each denomination.

I seriously dont know where to begin here.

Thank you

I think you mean that there is a total of 235 bills

A + b + c + d = 235
d = 2a
a + 10 = b

a + 5b + 10c + 20d = 2600

What does the b stand for in a+10=b? and how would I create a matrix out of this equation?