At the playground, 60% of the bike rack was filled. thisis 30 bikes. how many total slots are there for bicycles?

The most simplest way to explain this is by breaking down the 60%.

Think about it.

If 60% space = 30 bikes

then 30% space = 15 bikes

then 10% space must be 5 bikes.

So we now know for sure 60% space = 30 bikes.
And 10% space = 5 bikes.

Then we know remaining 40% space = 20 bikes.

So total space = 100% space, for 50 bikes.

The correct answer is d. (0,5)