Answer:
45.7
Explanation:
Hello there!
We can calculate the missing angle using trigonometry 
here are the trigonometric ratios
sin = opposite over hypotenuse 
cos = adjacent over hypotenuse 
tan = opposite over adjacent 
We are given x's opposite side length (8) and x's adjacent side length (7.8) 
we are given the information to use the trigonometric ratio tangent
so now we create an equation (remember tan - opposite over tangent)

now we solve for x 

we're left with 
 

finally we want to get rid of the tan 
To do so we take the inverse of tan (arctan^-1) and apply it to each side 

so x = 45.7252243
finally we round to the nearest tenth and get that the answer is 
45.7