How to do multiplication 2 digits by 2 digit

See step-by-step

Step-by-step explanation:

You take the numbers and put them directly on top of each other, above a line. Next, The second digit from the bottom number is multiplied by each of the digits from the top set, right to left. Now add a 0 under the result of the first set on the right side. Then you proceed to do it again but, with the next number from the bottom number. Right to Left. Last, add the numbers together, getting the final answer.

 10                                                                                                                                  x10                                                                                                                                                  

0x0=0  0x1=0        1x0=0   1x1=1

10                                                                                                                                  x10                                                                                                                                                  

   00

+100

100

a is the right answer

you didn't post any answer choices, so its not 100% clear what your teacher is looking for

however, log(15/7) is equivalent to log(15) - log(7)

i'm using the rule log(x/y) = log(x) - log(y)