The answer is A hope this helps
The <em>speed</em> intervals such that the mileage of the vehicle described is 20 miles per gallon or less are: v ∈ [10 mi/h, 20 mi/h] ∪ [50 mi/h, 75 mi/h]
<h3>How to determine the range of speed associate to desired gas mileages</h3>
In this question we have a <em>quadratic</em> function of the <em>gas</em> mileage (g), in miles per gallon, in terms of the <em>vehicle</em> speed (v), in miles per hour. Based on the information given in the statement we must solve for v the following <em>quadratic</em> function:
g = 10 + 0.7 · v - 0.01 · v² (1)
An effective approach consists in using a <em>graphing</em> tool, in which a <em>horizontal</em> line (g = 20) is applied on the <em>maximum desired</em> mileage such that we can determine the <em>speed</em> intervals. The <em>speed</em> intervals such that the mileage of the vehicle is 20 miles per gallon or less are: v ∈ [10 mi/h, 20 mi/h] ∪ [50 mi/h, 75 mi/h].
To learn more on quadratic functions: brainly.com/question/5975436
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If you mean "how to write the sum", the answer is

The result of this sum is
, because you start from 2 on the number line and take 3 steps to the left (negative integers mean going left, positive integers mean going right)
The error is in the second step they subtracted 3 from both sides but it was a 3x, which you can not do.
Correction.
9x+18+3x=1
12x+18=1
12x=-17
x=-17/12