2: (R2 + R1). Vout = Vin. R2

3: (-R2. Vin + R2) + R1. V out = 0

4: R2(-Vn +1) + R1.Vout = 0

5: R2 = (R1.Vout) / (Vin + 1)

How does one go from line 2, to line 3?

I end up with:

2: (R2 + R1). Vout = Vin. R2

3: (-R2. Vin) + R2. Vout + R1. Vout = 0

Could someone please explain?