The durations, $t$ minutes, of $242$ telephone calls made by one family over a span of $1$ week are set out in the frequency table below.
(i)[1]
Find the value of $a$ from the information provided.
(ii)[2]
Calculate an estimate for the mean length of these phone calls.
(iii)[4]
Using the grid, draw a histogram to show the data in the table.
(c(iii))[4]
Draw a histogram on the grid to represent the data in the table.
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