Okay, there is a right angle so that equals 90. A given angle inside the triangle is 35. To find the missing angel within the triangle you do 90+35 which will give you 125. You will then subtract 125 from 180 ( because all triangles add up to 180 ) so the angle missing at the top would be 55. Now, you’re going to want to use Sine, Cosine, and Tangent. I would use the angel 35 that they provided you. So the way you set it up will be -
Tan (35) = x / 12
Then you’re going to want to cross multiply so you will now have
X = tan(35) • 12
^ plug this equation into a calculator and you will get your answer. I hope this helped!