Question 1148772
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The two sides in the problem (one given, one to be found) are the opposite side and the hypotenuse.  The trig function relating those two sides is sine:<br>
{{{sin(x) = (opposite)/(hypotenuse)}}}<br>
Plug in the two known values to determine the third:<br>
{{{sin(20) = 45/x}}}<br>
Sin(20) is not a "nice" number; use a calculator.  (Make sure the calculator is using degrees and not radians....)<br>