When Lillian visited the riverbed, she used four different rocks known as speckled rocks, striped rocks, solid rocks, and spotted rocks to trade for things. However, she didn't know the value of each rock. Here's what she found out: A solid rock and a striped rock together equal 2 speckled rocks. A solid rock and a spotted rock together equal 3 speckled rocks. Based on this information, which of the following could Lillian conclude?