CREATE TABLE table_19703 ("Prefix size" TEXT, "Network mask" TEXT, "Available subnets" FLOAT, "Usable hosts per subnet" FLOAT, "Total usable hosts" FLOAT)

When the network mask is 255.255.255.252 what is the prefix size?
SELECT "Prefix size" FROM table_19703 WHERE "Network mask" = '255.255.255.252'
SELECT "Prefix size" FROM "table_19703" WHERE "Network mask" = '255.255.255.252'