Write the phrase as an algebraic expression. A number minus three. PLS HEL

Algebraic expression for a number minus three would be

x-3

The perpendicular bisector would be the line that connects with the line HI at a 90 degree angle and in the mid-point. This means that we would have to find the slope of the line HI and take the opposite. The slope of HI is 1/3. This means that the slope of the perpendicular line is -3. Now we must solve for the line that crosses through the midpoint. y=mx+b we know that m=-3 and that the midpoint is at -1,3 so x=-1 and y=3.  3=(-3)-1+b. We then solve for b and find it to be 0.  So the final answer is y= -3x