It's already reduced it remains as 69/80 because the is no greater common factor between the two.
Increasing the value of a would change the slope of the function specifically it would increase as well. Therefore, the line would be steeper than the original. The term ab represents the slope of the function and changing either one would result to the change of the steepness of the line.
Step-by-step explanation:
Multiplication of fractions is easiest operation. Simply multiple numerator to numerator and denominator to denominator. For example,

Addition and subtraction requires that we find a common demoninator.
For example,

The common denominator is 12. So I need to muliply each fraction to get the right denominator. 4*3 = 12.

Then we add the numerators

Then we should reduce.

Division is a little trickier because we have to flip-flop the second term and then multiply. For example: 
Answer: ±√2
Step-by-step explanation: A fraction is undefined when its denominator is =0 or undefined. so we need to get 2/3x²-6=0 or undefined. so we can also do 3x^2-6=0. Solving yields ±√2!