let x = orginal price of the shorts
$21 = x(100%-20%) * 1.05
$21 = x(80%) * 1.05
$21 = 0.8x * 1.05
Subtract 1.05 from both sides
$19.95 = 0.8x
Divide 0.8 from both sides
$24.9375 = x
So the orginal price of the shorts are about $24.94
What's 200 minus 50 that's your answer simple
5x + y = -13.....multiply by -3
4x + 3y = -17
-----------------
-15x - 3y = 39 (result of multiplying by -3)
4x + 3y = -17
-----------------add
-11x = 22
x = -22/11
x = -2
5x + y = -13
5(-2) + y = -13
-10 + y = -13
y = -13 + 10
y = -3
solution (-2,-3)