Homework Help: math need asap

Posted by SAP on Thursday, September 30, 2010 at 10:01pm.

7r-4s=-7 (7)
4r+7s=61 (4)

49r - 28s = -49
16r + 28s = 244
---------------
65r = 195
195/65 = 3 (simplified) (3, is the first number of the ordered pair.)

Now this is the part that I get lost on. I know I am suppose to substitute 3 into one of the equations above, but how do I determine which one. So if I substitute 3 into the 1st equation:

7(3)-4s= -7
21 - 4s= -7
------------
21 = -7 would my answer be -7/21

Substitute 3 into the 2nd equation:

4(3)+7s = 61
12 + 7s = 61
-------------
12 = 61 would my answer be 61/12

(3, is the first number of the ordered pair.)

(3,-7/21) or (3,61/12) which ordered pair is correct?

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