Answer:
A. B.
Step-by-step explanation:
Using proportions, the value of x that makes the triangle similar is of x = 14.
<h3>What is a proportion?</h3>
A proportion is a fraction of a total amount, and the measures are related using a rule of three.
In this problem, we want the triangles to be similar, hence the lengths of it's sides follow the proportion given next:

Applying cross multiplication:
6x = 12 x 7
x = 2 x 7
x = 14.
The value of x that makes the triangle similar is of x = 14.
More can be learned about proportions at brainly.com/question/24372153
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There are 21 red pens. For every 3 red pens, there is 1 blue pen.
Let's make these into a fraction equation.
21/p=3/1
p is the number of blue pens we have yet to find.
First, cross multiply.
21x1=21
px3=3p
Now, we have an equation of
21÷3p
We set it equal to 1, and we solve it.
21÷3p = 1
(21÷3p)×3p=1×3p
21=3p
21÷3=(3p)÷3
7=p
So, if there are 21 red pens, there are 7 blue pens.
We add these together to find the total number of pens the teacher has.
21+7=28
The teacher has 28 pens total.