You have a total of 21 coins that are nickels and quarters. the coins have a value of $2.25. how many quarters do you have?

 6

Step-by-step explanation:

Let n represent the quantity of nickels and q represent the quantity of quarters, then set up a system of equations and solve for q.

Quantity:  n  +    q  =  21    →    -5(n  +    q  =  21)    →   -5n    -5q  = -105

 Value:   5n + 25q = 225  →    1(5n + 25q = 225)  →    5n + 25q = 225

                                                                                              20q  = 120

                                                                                                   q  =  6

-7/8

step-by-step explanation:

instead of subtracting you add the -6/8 and -1/8

option (b) is correct

step-by-step explanation:

to find the solution of this system, we need to convert it into reduced row-echelon form. we have,

after applying row operations r2 -> r2/2 and r3 -> r3/3, we get,