First of all, you need to learn the rules.
It is against the rules of TSR to give the whole answer out. However, I will obviously help you to get the whole answer yourself, which is what I'm in the process of doing now.
y = mx + c is the form of a straight line graph, where x is the gradient and c is the y-intercept - where the line passes through the y-axis. To work out the gradient, you use the formula rise/run which is the vertical distance on the y axis / horizontal distance on the x axis. In this case, the question says:
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The diagram shows the graph y = 2x + 1.
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A line passes through the point (2, -3) and is perpendicular to y = 2x + 1.
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The equation of this line can be written in form ax + by = c.
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What are the values a, b and c?
This shows that the form is already given, we just need to work out some numbers. The co-ordinates of the other line is (2, -3) and it is perpendicular to the line y = 2x+1. Therefore, the gradient of the new line will be the gradient of -
m1, where m is the gradient of the original line. You can work out the gradient urself using that formula. Now, you can substitute the numbers given (co-ordinates) into the new line and work out y and x and therefore get c. This will give you the whole new equation of the line.