To find the change in Claire's weight, you need to subtract her final weight from her initial weight:
Initial weight in September: 187.4 pounds
Final weight in March: 163.5 pounds
Change in weight = Final weight - Initial weight
Change in weight = 163.5 - 187.4
Now, perform the calculation:
\[ 163.5 - 187.4 = -23.9 \]
The change in Claire's weight is -23.9 pounds.
Since the prompt asks for a DECIMAL value, the final answer is:
\(-23.9\)