What does "sierra del plata" mean?

Question 1 (fill-in-the-blank worth 1 points) fill the blank with the preterite tense of the verb in parentheses. yo a leer el libro ayer. (empezar) answer for blank 1: question 2 (fill-in-the-blank worth 1 points) fill the blank with the preterite tense of the verb in parentheses. ellos a trabajar. (empezar) answer for blank 1: question 3 (fill-in-the-blank worth 1 points) change this verb from the present tense to the preterite tense. yo empiezo answer for blank 1: question 4 (fill-in-the-blank worth 1 points) fill the blank with the preterite tense of the verb in parentheses. yo buena nota. (sacar) answer for blank 1: question 5 (fill-in-the-blank worth 1 points) change this verb from the present tense to the preterite tense. yo busco answer for blank 1:

Mary just sent out invitations to her wedding last week the invitations were so heavy that she put more than just one stamp on each envelope she used 255 stamps and mailed out 85 invitations and see you as an equal amount of stamps on each envelope

Answer the following question with a complete sentence using the cue in parentheses