<PRE><B>Question 147516</B>
7r-4s=7  eqn 1
4r+7s=69 eqn 2
This is 2 equations in 2 unknowns, r and s. You can solve for both r and s.
To eliminate one of the variables, you multiply both eqns by a number that will give the same coefficient for one of the variables. This is similar to finding the LCD, Least Common Denominator.
To eliminate the r terms, multiply eqn 1 by 4 and eqn 2 by 7.
----------
28r - 16s = 28
28r + 49s = 483
Subtract (2) from (1)
0r - 65s = -455
s = 7
----------
Substitute s into either eqn to find r.
7r -4*7 = 7
7r = 35
r = 5
----------
Check both eqns.
7*5 - 4*7 = 7 so eqn 1 is good.
4*5 + 7*7 = 69 so they both check.

</PRE>