I don’t quite seem to understand can you guys explain ?

Answer:
The answer is D
Step-by-step explanation:
Simplify the first inequality subtract 5 from 20
5t≤ −15
then divide
t ≤ -3
Simplify second ineqality
4t ≥ 20
divide
t ≥ 5
final answer :
t ≤ −3 or t ≥ 5