Question

the sum of 2, three times a number, -9, and four times the number

Answer 1

sum means add
let's say the number is n
3 times a number is 3n
4 times the number is 4n

so
sum of 2 and 3 times a number and -9 and 4 times the number means
2+3n-9+4n or
3n+4n+2-9 or
7n-7