解：4.2×3.6÷0.25，=15.12÷0.25，≈61（块）答：需要61块．
0.5*0.5=0.254.2/0.5=8.4=> 93.6/0.5=7.2 => 89*8=72需要72块
4.2×3.6/0.25≈61块
4.2x3.6÷0.25≈61(块)
