Let the number of column = x Number of rows = x + 4 Each bench is seated with 5 students. Two seats are vacant in class of 158 students. According to the statement, 5(x)(x+4)=158+2 5x2+20x=160 5x2+20x−160=0 x2+4x−32=0 x2+8x−4x−32=0 x(x+8)−4(x+8)=0 x=−8,4 x=4 Number of rows =x+4=4+4=8.