Hello from MrBillDoesMath!
Answer:
m = 0
b = 22
Discussion:
I will ignore the duplication of the point (15,22) and "y=mx+b" mentioned in this question.
A line parallel to the x axis is of the form
y = <constant>.
Since the line passes through (15,22), the above constant must be 22. That is,
y = 22 = 0x +22 = mx + b
so m = 0 and b = 22
Thank you,
MrB