If x + 4y = 5 and 5x + 6y = 7, then 3x + 5y = ?
Choose the correct choice from the following answers
A) 6  B) 5  C) 4  D) 3  E) 2

Rationale: add the left terms and right terms of the two equation to obtain a new equation x + 5 x + 4 y + 6 y = 5 + 7 group and simplify 6 x + 10 y = 12 divide all terms of the above equation by 2 to obtain a new equation 3 x + 5 y = 6 correct answer a
Answer: A