Congruent triangles always have at least 3 identical elements — like if both have a right angle, a 30° angle and a 12cm side.
We are given that these two are congruent in the text. We have two identical elements so far — angle of 35 and the side opposite the angle of 35 (which is what the little line in the middle means) — but we are missing that angle G.
Since angle G in the second triangle is in the same place as the angle of 79 in the first one (between the side with the line in it and the angle of 35), we know that angle will be also 79, given that the triangles are congruent (or identical, in other words). So your answer is 79°.
