For 7) you can just move the parenthesis around the 3.6 and 0.4 so that it would look like this :
(3.6 + 0.4) + 0.25
You can do the same thing for number 8 and make it
(2[tex] \frac{6}{10} [/tex] + [tex] \frac{4}{10} [/tex] ) + [tex] \frac{4}{5} [/tex]
