Sum of Summation Notation (PLEASE HELP!!!)

Hi Adam

$\displaystyle\sum_{n=4}^{10}\;(0.8n-0.4)\\~\\ \displaystyle\sum_{n=4}^{10}\;(0.8n)+\displaystyle\sum_{n=4}^{10}\;(-0.4) \qquad \text{that is 0.4 for (4,5,6,7,8,9,10)}\\~\\ =(0.8*4+0.8*5+......0.8*10) -( 7*0.4)\\ =0.8(4+5+6+7+8+9+10) -( 2.8)\\ =0.8(49) -( 2.8)\\ =36.4$