Question 773648
As his average his 74 in 4 tests, it means that 

sum of marks in 4 tests/4 = 74.
so, his total marks in 4 tests = 74 *4 = 296.

His average in 5 tests is 73. 
So, his total in 5 tests = 73 * 5 = 365.

His grade in the last test will be the difference between his marks in 4 tests and 5 tests. 

Therefore his grade in 5th test = 365 - 296 = 69.

:)