紧急!12月考 20135月SAT数学

If the circumference of a cir le is doubled when its radius r is increased by 4 inches, what is the value of r, in inches?

3y=2x-6  

y=1-cx

In the equations above,x and y are variables and c is a constant. If no ordered pair of numbers(x,y) satisfies both of the quations above,what is the value of c?

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