Question

Y = 2X + 1 has a gradient of 2 write the equation of a line parallel to it?

Answer 1

If the gradient is the same the line will be parallel. Your answer is Y=2x + 3 

Answer 2

paralell has same gradient (or slope)

y=mx+b
m=gradient

so the equation fo a line is y=2x+b and b can be any real number
like
y=2x+34234
y=2x+pi
y=2x+20/3
y=2x