The solution is as follows:
15% of 35 can be interpreted as: 15/100 times by 35, so 15(35) / 100 = 5,25
You also use the rule of three to find the solution by making this statement:
If a 100% => 35,
Then 15% => ?,
Therefore here, we times 15% by 35 and then divide by the 100%, which again gives us: 5,25