The unit rate for this case is the number of pieces Maria can learn per week. To find it we need to divide the number of pieces she already learnt by the number of weeks it took her to learn it.
She managed to learn 2 pieces per week. If she keeps this rate we can find the number of pieces she will be able to learn in 14 weeks, to do that we need to multiply the number of weeks by the unit rate, which is done below:
If she keeps this rate she'll be able to learn 28 pieces in 14 weeks.