How to find number of failed grades and the number of general average?

I have I table of students and their grades

How can I count the number of failed grades (<50) and find the general average ( I mean the average for every student ) using sqlite?

this is the table (studentTable):

sID LessonID grade
1     1      45
1     2      50
1     3      65
2     1      44
2     2      22
2     3      91

I expect the results like this:

sID  noOfFails   Average
1       1         53
2       2          5