Answer:
∠4 = 55°
∠6 = 35°
Explanation:
Finding the unknown angles:
 In ΔABC,
 35 + 90 + ∠4 = 180° {Sum of all angles of triangle}
 125 +∠4 = 180
 ∠4 = 180 - 125
  ∠4 = 55°
Linear pair: If in two adjacent angles, the non-common arms form a straight line, then the two angles are called linear pair and they add up to 180.
∠7 + ∠8 = 180° {linear pair}
 90 + ∠7 = 180°
 ∠7 = 180 - 90
 ∠7 = 90°
In ΔACD,
 ∠6 + ∠4+ ∠7 = 180 {Sum of all angles of triangle}
 ∠6 + 55 + 90 = 180
 ∠6 + 145 = 180
 ∠6 = 180 - 145
 ∠6 = 35°