Write an equation of the line that passes through the point (2, 3) and is perpendicular to the line y = 1/2x - 1

Perpendicular means opposite and reciprocal (in reference to the slope). 
The opposite of 1/2 is -1/2. The reciprocal of -1/2 is -2.

Now we know the slope we can plug the point they gave us into the X and Y positions to solve for b (in the point (2, 3) there is a X - Value (2) and a Y-value (3)

y= -2x+b
3= -2(2)+b
3= -4+b
1=b

Now we plug b and the slope in the generic y=mx+b equation:
y= -2x+1