Mark completes 14 projects at school per week for w weeks in a row. each week, his best friend mary completes half as many projects as mark completes. together, they complete 126 projects. which of the following is the number of weeks it took mark and mary to complete 126 projects?

For this case, the first thing we must do is define a variable.
 We have then:
 w: number of weeks.
 The equation for this problem is:
 14w + 7w = 126
 From here, we clear the value of w.
 We have then:
 21w = 126
 w = 126/21
 w = 6
 
 the number of weeks it took Mark and Mary to complete 126 projects is:
 w = 6

Idon’t know this and this isn’t middle school work