How do you simplify |-7 - 3|

You are making a battery for a science project. you have copper wire for your first electrode. you need to choose a conductor, a second electrode, and a device to plug into your battery. you have already chosen a lemon conductor. complete each statement below about the options that include a lemon conductor.

Icould really use some with this question.

The ratio of the measures of the three angles in a triangle is 2: 9: 4. find the measures of the angels