Answer: Joseph's residual is 1.86 (option d).
Explanation:
Hi, to answer this question we have to replace the variable "x" for Joseph’s age (23.5 months) in the equation given: 
y = 63.80 + 0.61x. 
y = 63.80 + 0.61 (23.5) 
y = 63.80 + 14.335 = 78.135 
Now, we subtract the amount obtained to Joseph's height ( 80 centimeters). 
Mathematically speaking: 
80 - 78.135 = 1.865 
So, Joseph’s residual is 1.86 (option d).