Answer:
75 degrees.
Explanation:
The total number of degrees in a triangle is 180 degrees therefore you can take the sum of the other 2 angles in the triangle and take that number and subtract it from 180.
1). 30+75=105
2).180-105=75
3). using the Side, Side, Side geometry rule, this means that both triangles are the same for all angles and side lengths
4). using the Alternative angle rule, the rule that say that a line that intersects 2 parallel lines forms 4 pairs of similar angles
5). therefore angle ABC is the same as angle BCD
6). Angle ABC was determined to be 75 degrees therefore angle BCD is also 75 degrees