Aparabola with vertex (1,-16) and y intercept (0,-15) crosses the x-axis in two places. one x-intercept is at (5,0). find the other x-intercept. separate values with a comma

The is a rule(pattern) to this problem, the pattern is to add 15 (+15)
Example: *0-15* you add 15 to zero to get 15 because 15+0=15!
Just like that *1-16* you add 15+1 to get 16. So the rule is keep adding 15!!

Can't really understand try to post again