What is the equation of the blue line?

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

What is the slope of the line shown below?

Rewrite the following quadratic functions in intercept or factored form. show your work. f(x) = 3x^2 - 12