A warehouse has dimensions of 20 meters by 30 meters and a roof with a total mass of 1.5×10⁴ kg. The roof is to be supported by vertical steel columns, each with a square cross-section of 20 cm by 20 cm. These columns will be evenly distributed along the longer sides of the warehouse. Given only compression and assuming a safety factor of 8, determine the number of columns required on each longer side of the warehouse and the spacing between each column. The compression strength for steel is 2.5×10⁸ N/m².