5a + 5b + 5c - 8x - 8y - 8z
All you have to do, is combine like terms. Let's go through it:

Arrange it so you can easily combine like terms:

So, your answer for the sum is 1) 7x² - 10x + 2
14(3+1) - (3 - 7)
"double" - times by 2
"and" - addition
when using " first second and third" you just have to assign the numbers by the way it comes in the problem...
first number - 7
second number - 3
third number - 1