For 45 hosts, the minimum subnet size must allow at least 46 usable addresses (1 each for network and broadcast addresses).
A /26 subnet provides 64 addresses, 62 usable - suitable.
A /27 subnet gives only 30 usable - insufficient.
A /25 offers 126 usable - more than needed.
A /28 provides just 14 - too small.
So, the most efficient subnet with minimal wastage is /26.
From Andrew Ramdayal's guide:
"When designing subnets, always choose the smallest subnet mask that still accommodates all hosts. A /26 provides 62 usable host addresses, suitable for networks with about 50 hosts."