Both lines are parallel so using the bottom line you are given angle 7 as being 80 degrees. Angle 5 and 7 form a straight line which is 180 degrees so angle 5 would be 180-80 = 100 degrees.
Angle 1 is the same as angle 5 so angle 1 is 100 degrees.
Answer: 100 degrees
(x/5)-6=2
It depends by difference of. Difference between is more specific.
Consider the following short explanation.
Answer: a1=15; d= -8.