Amount of the work done by Suzanne and Melody in one day = [1/10 + 1/15] of the work

Let x be the number of days that Suzanne and Melody worked together on the project (before Suzanne left)

Amount of the total work done in this time = x [1/10 + 1/15] of the work

After this, Melody worked for 5 days more.

Amount of the total work done by Melody in this time = 5[1/15] = 1/3rd of the work

As Melody finished 1/3rd of the work in the remaining 5 days, we can infer that together Suzanne and Melody finished 2/3rd of the work in x days

=> x[1/10 + 1/15] = 2/3

=> x = 4 days

The answer is choice (B)

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