Ineed to know the answers at the first line right but i didn't get four of the other ones right

What is best way to getting answer for my exam is

Determine the difference: 3.2 × 1010 – 1.1 × 1010. write your answer in scientific notation.

The value of x in this system of equations is 1. 3x + y = 9 y = –4x + 10 substitute the value of y in the first equation: combine like terms: apply the subtraction property of equality: apply the division property of equality: 3x + (–4x + 10) = 9 –x + 10 = 9 –x = –1 x = 1 what is the value of y?