What type of triangle is shown below?

The triangle that is shown in the attachment is called a right triangle because the angle of the triangle is 90°.  

The strategy to solve an angle in a right triangle 

1) Note that we are given the length of the side opposite to the missing angle, and the length of the hypotenuse. The trigonometric ratio that contains both of those sides is the sine. 

2) Create an equation using the sine of the missing angle.

3) Solve the equation for the missing angle using the sin⁻¹ function. 

The answer is d 18ft