Consider converting one currency to another using some exchange rate that can change.

$($a$)[16$ points$]$ Develop a class for the currency exchangers using Astah. The operations for this class should support $($i$)$ calculating the value of one currency given another, $($ii$)$ setting the exchange rate, and $($iii$)$ finding the exchange rate. The exchange rate has two decimal points. For the UML class provide name, definition, attributes, and methods; each attribute has a name, definition, type, and default visibility; each method has a name, definition, return value, and default visibility.

$($b$)[6$ points$]$ For each of the operations in part $($a$),$ determine and explain whether it is an action,

reaction, both, or something else.

$($c$)[15$ points$]$ Identify useful invariants, pre$-$conditions, and post$-$conditions for the operations given in part $($a$).$ All invariants, pre$-$conditions, and post$-$conditions must be formulated as Boolean

expressions. The pre$-$conditions and post$-$conditions should be useful for the operations