Sally is selling two types of seashells by the seashore. She is selling large and small shells. She sells small shells for 2 dollars each and large shells for 5 dollars each. She sold a combined 15 shells for total of 60 dollars. How many of each type of shell did she sell? Show your work.

A - 5 small shells and 10 large shells
B - 10 small shells and 5 large shells
C - 7 small shells and 8 large shells
D - 8 small shells and 7 large shells