已知二次函数f（x）=4x²-kx+12．

（1）若函数f（x）在区间[5，+∞）是增函数，求常数k的取值范围；

（2）若不等式f（x）＜4x的解为1＜x＜3，求常数k的值；

（3）若函数f（x）在区间[5，20]上的最大值为12，求常数k的值．

A certain truck manufacturer must have sales of $4.5 billion to break even this year. If the manufacturer had sales of $ 1.9 billion for the first half of the year, then, to break even for the year, its sales for the second half must be approximately what percent higher than its sales for the first half ？（）

A．11%

B．16%

C．27%

D．37%

E．58%