X=−6.58578643, −9.41421356 what is the rounded decimal of these two?

Depends on which place you're rounding to:

Step-by-step explanation:

Rounded to the tenths place (one number after the decimal point):

x = -6.6, -9.4

Rounded to the hundredths place (two numbers after the decimal place):

x = -6.59, -9.41

Rounded to the thousandths place (three numbers after the decimal place):

x = -6.586, -9.414

I don't think you'd need to round to the ten-thousandths place. If you do lemme know and I'll edit my answer. But you should know if the next digit is 5 or greater like in 15 you'd round up. If it's less than 5, you round down.