A, B, and C are three numbers. A is 2.5 times that of B. The ratio of B to C is 8:5. It is known that C is 4.5 smaller than A. What is the number of B?
甲乙丙三个数，甲是乙的2.5倍，乙与丙比为8：5，已知丙比甲小4.5，则乙数是多少．
<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<gadget id="calculator">4.5 / 15</gadget>
<output>0.3</output>

<gadget id="calculator">0.3 * 8</gadget>
<output>2.4</output>

<result>2.4</result>