50% of what number is 12.1?

50% = .50

"Of" means "multiply"

"What Number" .......we can let this be "N"

"Is" means "Equal To"

So we have

.50 * N = 12.1

Divide both sides by .50

N = 24.2

And that's it......

since 50% is equivalent to a half it is like asking 12.1 is half of what number.  That would be 24.2 since half of 24.2 is 12.1