Let's define the following variable.
x = Destiny's number of plums.
If Jennifer has 2/3 the number of plums Destiny has, then we can say that Jennifer has 2/3x plums.
If Andy has half as many plums as Jennifer, then we can say that Andy has 1/2 x 2/3x or 1/3x plums.
If Destiny has 13 more plums than Jennifer, then Destiny's number of plums x = 13 + 2/3x.
To calculate the total plums they have together, let's add them and solve for x first.