-30 and -30
-30 + -30 = -60
-30 x -30 = 900
900 is 60% of 1500
Add any number to (60 minus the same number).
960
Not too sure of your question but 15 is 25% of 60
60 + (-57) = 3
Number of seconds: 15 x 60 = 900 Number of 2-second intervals in 900: 900/2 = 450
900
900
It is: 900
1660
900/60 = 15 hours
60 x 900 = 54000