One Tool you can use in photo shop is the measure tool.
The measure tool lets you measure length, width, angle and location of areas in your image. If you scan something in a little crookedly, use this tool to measure the angle and then use "rotate canvas" to correct the rotation by the exact amount. To measure, choose the measure tool from the tool box. (It looks like a little ruler). Draw a line with it, and look at the info palette to see the angle, width, length and coordinates of your line. When you double click on the page, the line will disappear. Then go to Image > Rotate Canvas > Arbitrary. The amount of rotation needed to make a 90 degree angle will automatically be computed. Click OK.
This isn't really finished
and you don't fully explain how you perform the task here.
T: Please finish this task fully
explaining how you use the tool using step by step images.