Answer:
-3x^4 - 14x^3 + 3x^2 - 10
Step-by-step explanation:
You will have to use trig to solve this:
The side you have is adjacent to the known angle
The side you are looking for is opposite the known angle
^^^This means you need to use tan:
tan(24) = 
.445222 = 
^^^input tan(24) into calculator, then multiply 12 to both sides to isolate and solve for x
5.3 ≈ x
Hope this helped!

and you can expand the numerator if you wish, it won't be simplified further though.
Answer:
x² + 7x + 10 = 0
Subtract 10 from both sides
x² + 7x = -10
Use half the x coefficent (7/2) as the complete the square term
(x + 7/2)² = -10 + (7/2)²
note: the number added to "complete the square" is (7/2)² = 49/4
(x + 7/2)² = -10 + 49/4
(x + 7/2)² = 9/4
Take the square root of both sides
x + 7/2 = ±3/2
Subtract 7/2 from both sides
x = -7/2 ± 3/2
x = {-5, -2}