Given the Right Triangle shown in the exercise, you need to use the following Trigonometric Function in order to find the measure of "x":
[tex]tan\alpha=\frac{opposite}{adjacent}[/tex]
In this case, you can identify that:
[tex]\begin{gathered} \alpha=21° \\ opposite=x \\ adjacent=18 \end{gathered}[/tex]
Then, by substituting values and solving for "x", you get:
[tex]\begin{gathered} tan(21\text{\degree})=\frac{x}{18} \\ \\ 18\cdot tan(21\text{\degree})=x \end{gathered}[/tex][tex]x\approx6.9[/tex]
Hence, the answer is:
[tex]x\approx6.9[/tex]
