To solve a word problem quickly and correctly, make a note of what’s given and what has to be found.

Given:
X per day earning = $4
Y per day earning = $10
To find:
Number of weeks required by x to earn twice as much as Y.

We know that the amount that Y earns in 2 weeks can be calculated as 14 x 10 = $140
If X earns for P weeks, then, weekly earning for X = 7P
7P x 4 = 2 x 140
P = 10 weeks.

“a is twice as much as b” implies a = 2b and not a = b + 2b. If you had chosen

Option d): then you might have considered the equation as 7p × 4 = 140 + 2 × 140.
option b): then you might have considered the equation as 2 × 7p × 4 = 140
option c): then you might have calculated the amount that Y earns in 2 weeks as $ 20. Given that, employee Y earns $ 10/day. So for 2 weeks i.e. 14 days, Y earns $ 140
option a): then you might have considered the equation as 7p × 4 = 140. Notice the word “twice” in the question.