The pseudocode given below is $($incorrectly$)$ written to calculate and display the average of $2$ given numbers $($note that $/$ is used as the divide operator in programming$).$ Which of the following can be used to replace step $3$ so that the average is calculated correctly?

Figure $1\mathrm{.}14$

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a

Calculate average as $($number$1+$ number$2)/2$

b

Calculate average as $($number$1+$ number$2/2)$

c

Calculate average as number$1+$ number$2$