Answer:
OPTION B: K = 15
Step-by-step explanation:
The given equation is: 21 + 3x = 3x + K
Substitute K = 3x
we get: 21 = 3x + 3x + 3x
⇒ 21 + 3x = 6x
⇒ 21 = 3x
This gives the value of x = 7. That means K = 3x gives us a solution. So, OPTION A is eliminated.
Now, K = 15
The equation becomes 21 + 3x = 3x + 15
Subtracting 3x on both the sides, we get:
⇒ 21 + 3x - 3x = 15 + 3x - 3x
⇒ 21 = 15 which can not be correct. So, K = 15 renders the equation meaningless and hence with no solution.
So, OPTION B is the answer.
Note that K = 21 will give the equation with infinitely many solutions.
