7.2x5.8+0.72x42=7.2x5.8+7.2x4.2=7.2x（5.8+4.2）=7.2x10=72
7.2x5.8+0.72x42=7.2×5.8+7.2×4.2=7.2×（5.8+4.2）=7.2×10=72
