Hi, I'm happy to help!
First, we need to solve for x. We know that ABD is 78 degrees. (5x+3), and (5x-5) combined are also 78 degrees. So, we combine the like terms of these to get a new expression.
(5x+3) +(5x-5)
10x-2=78
From here, we want to single out the x, by editing both sides in the same way.
10x-2=78
+2 +2
10x=80
÷10 ÷10
x=8
Now that we know what x is, we can plug it in to the previous expressions to get the angles of ABC and DBC.
(5x-5)
((5·8)-5)
(40-5)
35
Now, we know that ABC is 35 degrees.
(5x+3)
((5·8)+3)
(40+3)
43
Now, we also know that DBC is 43 degrees.
To verify our answer we can add ABC and DBC together to check if it totals to ABD.
35+43=78
Now, we know that the answer: ABC is 35 degrees and DBC is 43 degrees is correct.
I hope this was helpful, keep learning! :D