assuming emp-id and sal tobe the fields in the 
table "Employee" followng query can be used

Select emp-id, sal from Employee where sal between "20000" 
and "50000"
OR
you have to run two different queries to extract records as 
selecting records above 20,000 would cover the second part 
too

2. select count (stud_id) from Student where 
course_name="Testing"

hope they would help

here they want number of employees not empno.
select count(empid),sal from emp where sal between 20000 
and 50000;

oh sorry i missed it..

thx for correcting me :-)

1.  select count(*)
    from employee
    where sal>=20000 and sal<=50000

2. select count(*)
   from student
   group by course