Answer:
k = 11.87
Explanation:
Because the two expressions should be equivalent, set the two expressions equal to each other.

Begin simplifying the equation and solve for k.
(distributive property)
(combine like terms - 7.77 + 4.1)
(add 10.5x to both sides to combine like terms -- the x values cancel out because -10.5x+10.5x = 0. Therefore, you are left with k = 11.87)