Mathematics problems

1.Need to calculate missing frequency

Class Interval Frequency
0-20. 19
20-40. F1 ?
40-60. 32
60-80. F2 ?
80-100. 19

Mean =50 N =120

2. Calculate the missing frequency

In the following frequency distribution if thr median of the distribution is Median = 56.75

Class Interval. Frequency
20-30. 4
30-40. 16
40-50. 26
50-60. 50
60-70. F ?
70-80. 18
80-90. 12
90-100. 2

Would require you to solve both the sums with proper explanation and formulas.