Why do you have to do natural log as the first step to this problem instead of log?

You don't have to, log to the base 10 will give the same result.   Try it using your calculator and you'll get the same answer for both logs.

step-by-step explanation:

i believe its "c" because all of the other options include a but it could be d because there is a way of financing with cash at certain places but its uncommon.

m∠a is 90°

m∠b is 40°