计算。500-(240+38×6); (845-15×3)÷16
45.55-(6.82+15.55) 34.52-17.87-12.23
(×+)÷ ÷[(+)×]
(+)×15×11 37.5+19.5÷(2.5×4)
12×103-4500÷75 ×[÷(×)]
×+÷