CREATE TABLE table_204_131 (id DECIMAL, "tops design code" TEXT, "electrical system" TEXT, "max speed" TEXT, "weight" TEXT, "brakes" TEXT, "route availability" DECIMAL, "notes" TEXT)

how many times is 90v listed as the electrical system ?
SELECT COUNT(*) FROM table_204_131 WHERE "electrical system" = '90 v'
SELECT COUNT(*) FROM "table_204_131" WHERE "electrical system" = '90 v'