Final answer:
The membership fee for the sports club in 2018, after a 9% increase, was $78.48.
Step-by-step explanation:
The 2017 sports club membership fee was $72, and it was increased by 9% in 2018. To find the fee in 2018, you calculate 9% of $72 and add it to the original fee. A 9% increase on $72 is $6.48 (0.09 x $72), so the new fee is $72 + $6.48, which equals $78.48.