Hi there!
In order to answer your question, you'll need to use the cross product method:

(100 × 270) ÷ 1,800 = X
27,000 ÷ 1,800 = X
15 = X
= 15%
Your answer is: Isaac put 15% of his earnings into his savings.
There you go! I really hope this helped, if there's anything just let me know! :)