Question

If x + 4y = 5 and 5x + 6y = 7, then what is the value of 3x + 5y?

Answer 1

• Option D

Step-by-step Solution:

• => x + 4y = 5

5x + 6y = 7

• => 3(x + 4y = 5)

2(5x + 6y = 7)

• => 3x + 12y = 15

10x + 12y = 14

• => 3x + 12y = 15

-10x - 12y = -14

• => -7x = 1
• => x = -1/7
• => x + 4y = 5
• => -1/7 + 4y = 5
• => 4y = 5 + 1/7
• => 4y = 35/7 + 1/7
• => 4y = 36/7
• => y = 9/7
• => 3x + 5y
• => 3(-1/7) + 5(9/7)
• => -3/7 + 45/7
• => 42/7
• => 6

Hence, Option D is correct.