In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data
∠ ADB = 3a + 10
∠ BDC = 13a
DA and DC are perpendicular
Step 02
Graph
Step 03:
(3a + 10) + 13a = 90
16a + 10 = 90
16a = 90 - 10
a = 80 / 16
a = 5
m ∠ ADB = 3a + 10 = 3*5 + 10 = 15 + 10 = 25°
m ∠ BDC = 13a = 13 * 5 = 65°
The solution is:
a = 5
m ∠ ADB = 25°
m ∠ BDC = 65°