The way to do this problem is to compute the equation of the line through (1,0) and perpendicular to y=2x+3.
Then solve the system of two linear equations (the original equation and the perpendicular); this will give you the intersection of the two lines. Then compute the distance from (1,0) to the intersection point.
HOWEVER, there is a general solution to this problem which I will given you:
The distance from a point (x1,y1) to the line ax + by + c = 0 is given by
d = (ax1 + by1 + c)/sqrt(a2 + b2).