解:(1)(3

+4


)÷(1-

),
=[6+(

)]×36,
=6×36+(

)×36,
=36×6+36×

+36×

-36×

,
=216+30+20-9,
=257;
(2)999.8×98+(

-0.6)×9998,
=999.8×98+0.2×9998,
=999.8×98+2×999.8,
=999.8×(98+2),
=999.8×100,
=99980;
(3)[(3

-3

)×1.5+2.45]×(1.9-

),
=[

×1.5+2.45]×1,
=[0.05+2.45]×1,
=2.5;
(4)(0.5x+4

):

=x:0.6,
0.7x=0.6×(0.5x+4.5)
0.7x=0.3x+2.7,
0.7x-0.3x=0.3x-0.3x+2.7,
0.4x=2.7,
0.4x÷0.4=2.7÷0.4,
x=6.75.
分析:(1)、(2)运用乘法的分配律进行计算即可.
(3)我们按照四则混合运算的剩下进行计算,先计算中括号内部的小括号,再就是中括号内部的,最后计算中括号外面的.
(4)我们运用比例的基本性质进行解答即可.
点评:完成本题要注意分析式中数据,运用合适的简便方法计算.同时考查了比例基本性质的掌握与运用情况.