<u><em>Answer:</em></u>
<u>The simplest form would be:</u>
8c² - 1.5d
<u><em>Explanation:</em></u>
To simplify an expression, we need to <u>gather the like terms</u>.
Like terms are the ones having the same variable raised to the same power
<u>In the given expression:</u>
6c² + 2.5d - d + 2c² - 3d
We have terms having c² and terms having d.
<u>Therefore, we would gather them as follows:</u>
6c² + 2.5d - d + 2c² - 3d
(6+2)c² + (2.5-1-3)d
8c² - 1.5d ......................> This is the simplest form
Hope this helps :)