I need help solving the following problem. I need the find the values of m and b.

limit x->0 [(root mx + b) - 3 ] / x = 1

I tried rationalizing this which was multiply by (root mx + b) + 3 on both the denominator and numerator, but then I do not know where to do from here. I cross multiplied the denominator with the 1, and my teacher said it was wrong. Please help!