Given tan A = 3/4, which angle is A?

Since tanA = opp/adj = 3/4   ....then angle A  must be  "1" in the diagram

For a right triangle, the tangent of the two acute angles is defined to the length of the opposite side divided by the length of the adjacent side.

tan = opp / adj

If tan A = 3/4, the opposite side is the 3 ft side, the adjacent side is the 4 ft side. The angle that fits this criterion is angle 1.