Final answer:
Grandma Millie's total change in height over 3 years is 3/4 cm.
Step-by-step explanation:
To find Grandma Millie's total change in height over 3 years, we need to multiply her height decrease per year by the number of years. Since her height decreases by 1/4 cm each year, we multiply 1/4 cm by 3 years:
1/4 cm × 3 years = 3/4 cm
Therefore, Grandma Millie will have a total change in height of 3/4 cm over 3 years.