Let's begin by listing out the information given to us:
This is an equilateral triangle; this means that all the angles in the triangle are equal
The sum of angles in a triangle is 180 degrees
We calculate x thus:
[tex]\begin{gathered} (10x+20)=180 \\ \text{Subtrract 20 from both sides, we have:} \\ 10x+20-20=180-20 \\ 10x=160 \\ \text{Divide both sides by 10, we have:} \\ \frac{10x}{10}=\frac{160}{10} \\ x=16 \end{gathered}[/tex]