Question 853286
<pre>
2.2+8.8+15.4+...

8.8-2.2 = 6.6
15.4-8.8 = 6.6

d = 6.6
a<sub>1</sub> = 2.2

nth term = a<sub>1</sub>+(n-1)d = 2.2+(n-1)(6.6) = 2.2+6.6n-6.6 = 6.6n-4.4

{{{sum((6.6n-4.4),n=1,5)}}}

That's probably as far as you were expected to take it, but
it can be simplified as

{{{sum((6.6n),n=1,5)+sum((-4.4),1,5)}}}{{{""=""}}}{{{6.6sum((n),n=1,5)-4.4sum(1,1,5)}}}{{{""=""}}}{{{6.6sum((n),n=1,5)-4.4(5)}}}{{{""=""}}}{{{6.6sum((n),n=1,5)-22}}}

Edwin</pre>