A nationwide parcel delivery service keeps track of the number of late deliveries $($more than $30$ minutes past the time promised to clients$)$ per day. They plan on using a control chart to plot their results. Which type of control chart$($s$)$ would you recommend?

Question $6$ options:

a$)$

x$-$bar, but not R$-$charts

b$)$

both p$-$ and c$-$charts

c$)$

c$-$charts

d$)$

x$-$bar and R$-$charts

e$)$

p$-$charts