a) average rate of change =
\(\frac{\text{change in f(x)}}{\text{change in x}}\,=\,\frac{f(1)-f(2)}{1-2}\,=\,\frac{(\,2(1)^3-3(1)\,)\,-\,(\,2(2)^3-3(2)\,)}{1-2}\,=\,\frac{(-1)-(10)}{-1}\,=\,\frac{-11}{-1}\,=\,11\)
like helperid said.
b) We want an equation of a line that has a slope of 11 and passes through the point (1, f(1) )
And (1, f(1) = (1, -1)
So.. the equation in point-slope form is y + 1 = 11(x - 1)
And in slope intercept form, it is y = 11x - 12
c) Find the average rate of change between the points x = a and x = a + h .
Thie is the same as part a , just with letters in place of numbers. 
average rate of change =
\(=\,\frac{\text{change in f(x)}}{\text{change in x}}\\~\\ =\,\frac{f(a+h)-f(a)}{(a+h)-(a)} \\~\\ =\,\frac{(\,2(a+h)^3-3(a+h)\,)\,-\,(\,2(a)^3-3(a)\,)}{h} \\~\\ =\,\frac{2(a+h)^3-3(a+h)-2a^3+3a}{h} \)
I don't know if you need it more simplified than that.
