For this case we have that by definition of trigonometric relations of a rectangular triangle, that the cosine of an angle is given by the leg adjacent to the angle on the hypotenuse of the triangle. Then, according to the figure we have:
![cos (53) = \frac {18} {x}](https://img.qammunity.org/2020/formulas/mathematics/high-school/u1wcmw0vzb6mquvc15fojtknkgcho20q5c.png)
Clearing x:
![x = \frac {18} {cos (53)}\\x = \frac {18} {0.60181502}\\x = 29,9095226969](https://img.qammunity.org/2020/formulas/mathematics/high-school/xvo91wvoyb9wvvucdogvymwqxjb7kwxgsm.png)
Rounding:
![x = 29.91](https://img.qammunity.org/2020/formulas/mathematics/high-school/z75t6g4tj4qx0cv66v3is0lf56x9mobuas.png)
Answer:
29.91