Elizabeth has 1 and 7/10 as many plants as Rosalie, so she has more plants than her, since the fraction is greater than one. So that means you need to take the number of plants Elizabeth has and divide it by the fraction.
51 / (1 7/10) = 30
To do this, remember to make both sides into a mixed number fraction, flip the second fraction, and then multiply them together. So 1 and 7/10 becomes 17/10 and 51 becomes 51/1. Then flip 17/10 and multiply.
