Note: This is done in the interior triangle as the angle will be equivalent to the other two angles.
Here's how you solve it:
You have to use the law of cosine for the interior triangle; the law of cosine is: c^2 = a^2 +b^2 - 2ab times cos (C)
Substitute each factor so that the equation now appears as so:
h^2 = 8^2 + 10^2 - 2(8)(10) times cos (80)
This will give you: h = 11.67
Now, you have to apply this to the law of sin which is a over sin(A) = b over sin (B) = c over sin (C). (Lowercase letters are the opposite side of uppercase angles.)
This will then give you:
11.67 over sin (80) = 8 over sin (S) = 10 over sin (T)
sin -1 ((8 times sin (80)) over 11.67) is equal to S
sin -1 ((10 times sin (80)0 over 11.67)) is equal to T
Because you now know the angles of S and T, you need to use the law of sin again.
t over sin (T) = s over sin (S)
t = 10 + x s = 8 + 18 = 22
Thus, you need to substitute the variables to get this equation:
10 + x over sin (57.54) = 22 over sin (42.45)
x = 22 times sin (57.54) over sin (42.45) and next to this is -10