Given an IP, 24.15.19.2 with /24 subnetmask.Give the subnetmask and
network address. Also given the same IP, how many subnetmask can be
made with /26 and how many IPs does that leave?

1) 24.15.19.2/24

subnet mask - 255.255.255.0
network address - 24.25.19.0

2) 24.15.19.2 / 26

I think the 2nd question should be how many subnets instead of subnet mask.
if i am right,

normally it should be 2 subnets.

but the IP address 24.15.19.2 /26 is in the zero subnet, for which, in
CISCO devices we need to have "ip subnet-zero" command issued in the
CLI.
This command  will make the above IP address a valid one since it
makes the zero subnet valid (normally it is not)in both the cases, the
number of IPs should be 62.

Please let me know if you need more explanations on this

Thanks for the answer

You are welcome!