Put the equation in desmos and you will get your answer :)
Answer:
642,000,000,000,000,000,000,000 kg
Step-by-step explanation: Basically you are multiplying 6.42 by 100,000,000,000,000,000,000,000. That looks really intimidating but it is very simple. All you have to do is move the decimal 23 hops to the right. Moving it to the right makes the number big, were moving it to the left makes the number smaller. We want a bigger number because we are writing the number in standard notation. Right now it is in scientific notation form (scientific notation is used because it is easier and quicker to write than writing 21 zeros).
Answer:
B 405
(=20*9 + 25*9)
what are the blue-ish dots on your screen? :|
I like to reduce everything by half if I don't already know the answer.

It just so happens that is the reduced fraction.
All I did was halve 18, which is 9, and halve 34, which is 17.