A would be the answer because Li bought 5 earrings and 1 necklace while Jen bought 1 earring and 2 necklaces.
So technically Li bought 5 e's and 1 n while Jen bought 1 e and 2 n's(to make it easier to understand i explained with the variables)
So Li's equation would be 5e+n=75(her total cost)
And Jen's equation would be e+2n=51(her total cost)
Hope this helped!