Answer:
4 interval of six months.
Step-by-step explanation:
Given: Joe earn $14 per hour
Blaine earn $18 per hour.
Joe receives a raise of $1.75 every six months
Blaine receives a raise of $0.75 every six months.
Lets assume the number of six month intervals be "x".
Now, finding the number of six months interval require to get Joe´s earning equal to Blaine earning.
Forming an equation to find the six month interval
⇒ 
Solving the equation to find the value of x
⇒ 
subtracting both side by 0.75x
⇒ 
subtracting both side by 14
∴ 
Subtituting the value of x, we will get both Joe and Blaine earning as equal.

⇒ 
⇒ 
Hence, after 4 interval of six months, Joe to earn same hourly rate as Blaine.