How do I do this? I can't remember how and Algebra 2 has always been a struggle for me

Step-by-step explanation:

This is a piecewise function. If we are finding the average rate of change over the interval 4 and 12 inclusive, that means that we are finding the slope of the whole function (both pieces) from 4 to 12 (domain values are from 4 to 12. That means x values). This is not a straight line, so the average value is merely a rough estimate of the slope between x values 4 and 12.

When x ≤ 4, we have to use the first piece of the function, 3x - 7 because the restriction on the domain is that x has to be less than 6 and 4 is less than 6. Evaluating at the domain of 4 in the first piece will give us an (x, y) coordinate to help find the slope.

f(4) = 3(4) - 7 and

f(4) = 12 - 7 so

f(4) = 5 and the coordinate is (4, 5).

When x ≤ 12 we have to use the second piece of the function, .75x + 10 because the domain restriction is that x has to be greater than or equal to 6 and 12 is greater than 6. Evaluating at a domain of 6 will give us the other coordinate we need to find the slope.

f(12) = .75(12) + 10 and

f(12) = 9 + 10 so

f(12) = 19 and the coordinate is (12, 19). Now for the slope (aka average rate of change). Using the slope formula:

There you go! Just remember the domain thing and you should be fine.

18a

step-by-step explanation:

simply because it is. it's the highest common factor