Answer:
Rob saved $30 while he earned $75.
Step-by-step explanation:
Given:
For every 15 dollars he earns babysitting, he saves 6 dollars.
For money earned = $15
Money saved = $6
We will first find the percentage amount saved by rob
Percentage of amount is calculated by dividing money saved with for money saved and then multiplied by 100.
Percentage amount saved = 
Now we need to find the amount of money save when money earned $75.
Amount of money saved can be calculate by multiplying money earned with percentile amount saved.
Framing in equation form we get;
Amount saved = 
Hence Rob saved $30 while he earned $75.