grade 9 math!!!!!!!!!! please help
posted by selena .
lavre has sixtyone coins, all of whichare dimes and quaters. if the total value of the coins is $9.85, how many of each kind of coins has she?

If Q = # quarters
and D = # dimes.
Then
Q+D=61
.25Q+.10D=9.85
=================
Two equations and two unknowns. Solve for Q and D. Check my work. 
Q = 25
D = 36
It's a system of linear equations so you can put it into a matrix to solve
let Matrix A be a 2x2 matrix
1 1
.25 .1
and have another matrix, B
61 
9.85
A^1 * B will give you the answer