I don't understand what I'm doing wrong with these Chemistry problems

Here are a couple problems I can't figure out.
6.071 X 10^-5-8.2 X 10^-6-0.521 X 10^-4 I got76 X 10^5 but that's Wrong, I'm not sure what I'm doing wrong, if you could write out the steps that would help me so much. The other one is:
(3.8 X 10^-12+4.0 X 10^-13)/(4 X 10^12+6.3 X 10^13) I got 0.75 X 10^7 but that's wrong too. if you could give me the steps to this one it would really help me understand this better, thank you.

6.071 X 10^-5 - 8.2 X 10^-6 - 0.521 X 10^-4
Enter this into your calculator as:- It is important to use the brackets:
(6.071 X 10^-5) - (8.2 X 10^-6) - ( 0.521*10^-4) = 4.1 X 10^-7

(3.8 X 10^-12+4.0 X 10^-13)/(4 X 10^12+6.3 X 10^13)
(4.2 X 10^-12) / ( 6.7 X 10^13 ) = 6.27 X 10^-26

convert all the indices to 10^-5 then bring then remove the common factor
I.e 6.071*10^-5 - 0.82*10^-5 - 5.21*10^-5
Removing 10^-5 you got
(6.071 - 0.82 - 5.21)*10^-5
Subtracting the decimal value in the bracket you got
0.041*10^-5 = 4.1*10^-7
If you apply this rule for the 2nd question by making the numerator 10^-13 and denominator 10^13 you will got 6.56*10^-26

You'll need to use a Scientific Calculator.
Now, take 6.071X10^5 Now see the problem?
You'll need to break it down time after time when you perform the Math. You'll need to do it on the left and work your way towards the right.
Remember, Scientific Calculator.

You have mental problems.