Answer:
The equation of new line is (y-3)=2(x-10).
Explanation:
If a line passing through the point (x₁,y₁) with slope m, then the point slope form of the line is

It is given that Alejandra correctly wrote the equation

Here,

It means the slope of the line is 1 and the line passing through the point (10,3).
The teacher then changed the line so it had a slope of 2, but still went through the same point.
Now the slope of line is 2 and the line passing through the point (10,3). So the point slope form of the line is

Therefore the equation of new line is (y-3)=2(x-10).