Plz I need some help with 11-12 . My teacher didn’t even explain it correctly so now I’m confused.

Answer:
Step 1: Transpose everything to one side
12. x²+16x+15-10x+4=0
Step 2: Add the like terms
x² + (16x - 10x) + 15 + 4=0
x² + 6x + 19=0
Step 3: Use the quadratic formula to get the value(s) of x.
a=1 b=6 c=19
[tex]x = \frac{ - b + - \sqrt{b {}^{2} - 4ac } {}^{} }{2a} [/tex]
therefore, x=... or x