CREATE TABLE table_51481 ("Driver" TEXT, "Constructor" TEXT, "Laps" FLOAT, "Time/Retired" TEXT, "Grid" FLOAT)

How many laps were there when time/retired was gearbox?
SELECT SUM("Laps") FROM table_51481 WHERE "Time/Retired" = 'gearbox'
SELECT SUM("Laps") FROM "table_51481" WHERE "Time/Retired" = 'gearbox'