Which method is most efficient in solving a system of linear equations when the two equation have x-values with opposite coefficient values a. guess and check b. graphing c. substitution d. elimination

D) Elimination

For example, consider the system of equations below
2x+3y = 9
-2x+6y = 18
Adding straight down will have the x terms (2x and -2x) add to 0x which is just 0. The x terms will go away. In this case, the 2 and -2 are opposite coefficient values for the x terms.

Letter a i would say