The most important thing you can do on the test is follow the directions to the letter. If you familiarize with a calculator you can insert the appropriate numbers into the appropriate formula to get the correct answer fairly quickly. The choices were also spread out enough that the correct answers are fairly apparent. The most important thing is to pick apart every question and possible answer to your complete satisfaction just answer the ones you are comfortable with first then work through the ones you can handle next and then in the last 5min or so guess at the rest. 72% gives you a pretty wide margin for error. You need to become comfortable searching out the answers, you need to learn to use the index/tables and tabs to search out the answers.   Good Luck you might need it

There is a shortcut, but if you are using it for the exam, I hope you fail! (Reported Carbon content plus the reported Manganese divided by 15 will give you a rough number.)