What should come in place of the question mark (?) in the following questions?

Let's denote the unknown percentage as "x."

So, the equation becomes:
x% of 280 + 18% of 550 = 143.8

Now, calculate each part of the equation:
x% of 280 = (x/100) * 280
18% of 550 = (18/100) * 550

Now, the equation becomes:
(x/100) * 280 + (18/100) * 550 = 143.8

Now, simplify the equation:
(2.8x) + (99) = 143.8

Subtract 99 from both sides of the equation:
2.8x = 143.8 - 99 2.8x = 44.8

Now, divide both sides by 2.8 to solve for x:
x = 44.8 / 2.8 x = 16

So, the value that should replace the question mark is 16.
The correct option is (d) 16.