Help with system of equations!!!?

Question

I need help solving this system of equations:

D+Q=15
.10D+.25Q=2.85

Answer 1

D+Q=15-------------1

.10D+.25Q=2.85------------2

multiply by 10 equation 2.

        D+Q=15-------------3

  (-)   D + 2.5Q =28.5-----------4

   --------------------------------

            - 1.5 Q= - 13.5

   divide by - 1.5 in the euation

                  Q = -13.5 / - 1.5

                  Q = 9

substitute Q=9 in the equatin 1

   D + 9 = 15

subtract 9 from each side

  D + 9 - 9 = 15 -  9

            D = 6

the solution is (D ,Q ) = ( 6 ,9 )