Statement (1) We have two variables and one equation so we cannot determine the value of either variable. They could be any two non-zero single-digit numbers whose sum is 10. This statement alone is not sufficient.
The correct answer is B, C, or E.
Statement (2) Two values of x satisfy this statement: 91 and 80. This statement alone is not sufficient.
The correct answer must be either C or E.
Statement (1 & 2) We have two equations and two variables, which we can solve by substitution or combination to find each variable. The statements together are sufficient.
Alternately, of the two possible values of x from statement (2), only one satisfies both statements.
The correct answer is C.