Model B correctly displays sienna's and jacob's equations.
For sienna, the $8 can be represented as 8 unit blocks, which is displayed in model 2. The $3 per week can be represented as 3 x tiles, as shown in the picture, because it represents how many weeks.
For jacob, the model shows 6 unit blocks which represents his 6 dollars. The $4 per week is represented with the 4 x tiles, and we use x tiles because we are calculating how many weeks.