It sounds like you want to solve for x. If so, then follow these steps:
2x-1 = r
2x-1 = 4x ... replace r with 4x
2x-1-2x = 4x-2x ... subtract 2x from both sides
-1 = 2x
2x = -1
2x/2 = -1/2 .... divide both sides by 2
x = -1/2 is the fractional solution for x
x = -0.5 is the decimal solution for x.
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If you want to figure out the value of r, then plug the x solution into the equation below and simplify
r = 4x
r = 4(-1/2)
r = -2
