We can see that the triangles are similar, so we can formulate the following equation:
[tex]\begin{gathered} \frac{6}{21}=\frac{8}{3x+10} \\ \frac{6}{21}\cdot(3x+10)=8\text{ (Multiplying by 3x+10 on both sides of the equation)} \\ 6\cdot(3x+10)=8\cdot21\text{ (Multiplying by 21 on both sides of the equation)} \\ 18x+60=168\text{ (Distributing and multiplying)} \\ 18x=168-60\text{ (Subtracting 60 from both sides of the equation)} \\ 18x\text{ = 108 (Subtracting)} \\ x=\frac{108}{18}(\text{ Dividing by 18 on both sides of the equation)} \\ x=6\text{ (Dividing)} \\ \text{The answer is }x=6 \end{gathered}[/tex]
