Using IF AND and multiple conditions

I need to create a formula to identify the tier based on the following conditions:

1. Result Conditon1 Condition2
2. tier_1 >=61 >=300001
3. tier_2 >=25 - <=60 >=100001 - <=300000
4. tier_3 <=24 >=0 - <=100000

I have created individual formulas but I can't put them together

=if(and(B19>=61,B1823>=300001),"Tier 1")

=IF(and(B18>=100001,B18<=300000,B19>=25,B19<=60),"Tier 2")

=if(and(B19>=0,B19<=100000,B18<=24),"Tier 3")

Your help is greatly appreciated.

Thank you, Carlos