CREATE TABLE table_55507 ("PRR Class" CLOB, "Builderpars_m_singles Model" CLOB, "Build date" CLOB, "Total produced" FLOAT, "Wheel arrangement" CLOB, "Service" CLOB, "Power output" CLOB)

What PRR class has a Wheel arrangement of a1a-a1a?
SELECT "PRR Class" FROM table_55507 WHERE "Wheel arrangement" = 'a1a-a1a'
SELECT "PRR Class" FROM "table_55507" WHERE "Wheel arrangement" = 'a1a-a1a'