Answer:

Step-by-step explanation:
In a right triangle the tangent of an angle is the ratio of the opposite length over the adjacent*. In formulas,
Solving for x, using a calculator for the tangent, 
*I promise I didn't just spellcheck that.
To determine the fourth term, plug 4 into the equation;
Think of sea level as 0 on number line
-13 + 6 - 15
Answer:
12 in
Step-by-step explanation:
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X equals 60 degrees (80-20=60)