The answer would be 70 degrees.
In order to find this answer, we must first look at the cos value of an angle. The unknown angle here gives us an adjacent side of 3.4 and a hypotenuse of 10. Thus, we can use the following with cos.
Cos(A) = 3.4/10 or Cos(A) = .34
As a result, we can then use the arccos function to find the answer.
acrcos(.34) = A
70.12 = A
Then when we round, we'd get 70.