What is 7.09x10 to the 5 minus 6.10xto the 4 in scientific notation

When subtracting scientific notation, you first need to make the exponents the same. The standard is to make the smaller exponent the same as the higher one.
Let's take a look at your given:


This is smaller. 

Every time you add to the exponent, you need to move the decimal. So to make it the same, you need to add 1 to the 4 to get 5. Then move the decimal to the left. Your new notation would be:


Then you just line up the decimal as you would before subtracting and just copy the base and exponent.

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Maybe you should get some from your teacher and learn more so you can get your grades up and maybe study a bit more