Begin by subtracting 5 from both sides to get the z term by itself. This gives you:
2z>=1470
Then divide by 2 on both sides to get z by itself. This will give you:
color(red)(z>=735)
This can be checked by picking a value greater than 735 and a value less than 735 and testing them against the original inequality.
For example, let's try 600 and 800.
600 is less than 735, so the inequality shouldn't work.
2z+5>=1475
2(600)+5>=1475
1205>=1475 -- which is not true.
As for 800, this should work because it is greater than 735.
2z+5>=1475
2(800)+5>=1475
1605>=1475 -- which is true.