We know that a line is perpendicular to another line if one slope is the opposite reciprocal of the other. So, the slope of the line perpendicular to y=1/2x-3 would by -2/1 or -2. Now, to find the y intercept, plug in the coordinate (1, -1) to the equation y = -2x + b.
-1 = -2(1) + b
-1 = -2 + b
1 = b
Now we know the y intercept and slope of the new line, which is enough to make the equation. y = -2x + 1 is your answer.
Hope this helps!! :)