In this question, let's add those polynomials
(5x-6) + (2x-6)
5x -6 +2x -6 <em>Combine like terms</em>
<em>5x +2x -6-6</em>
7x -12
Since this is not an equation, no further step can be done.
The number you need is 16 all you have to do is work out the problem and try to understand it they are trying to confuse you don't need an equation.
Hope this help!
Have a Great day mate !!
D/H = 0.25
18/H = 0.25/1
Cross multiply and solve for H