Answer:
The answer is D.) 5d+9d = 300 + 4d
Step-by-step explanation:
The equation states that for each day he attends to the gym to swim and exercise without a membership he has to pay for both, which is $5 and $9 respectively. This is each day that he attends.
However, if he HAS a membership, he only has to pay the $300 yearly fee once, and then $4 everyday he attends afterwards to do both swimming and exercising.
Now, in order to find out when the membership is worth it you need to find out when the membership cost and the non-membership cost is equal. so on one side of the equation you'll need the non-membership costs, and on the other side we'll put the membership cost.
So, for the non-membership cost, every day he goes it'll cost him $5 to swim and $9 to exercise, meaning that one side of the equation is 5d (d represents days) + 9d
And for the membership side we have the $300 initial, one-time fee, and then the $4 a day he has to pay to attend. This is equivalent to 300+4d
Finally, we put both equations together in a way to show that we want both sides to be equal, i.e
5d+9d = 300+4d
Thus our answer is D