Subnetting without the panic
Most people fail subnetting questions because they try to do binary arithmetic under time pressure. Here is the pattern that removes the arithmetic.
Subnetting is the topic that makes people abandon the CCNA. It should not be. The reason it feels hard is that most explanations teach it as binary conversion, which is slow and error-prone when you have ninety seconds per question.
The faster approach is to memorise one row of numbers: 128, 192, 224, 240, 248, 252, 254, 255. That is every possible value of a subnet octet. Each one corresponds to a block size: 128, 64, 32, 16, 8, 4, 2, 1.
Given 192.168.10.0/26, the mask is 255.255.255.192. The interesting octet is the last one, 192, which is the second entry, so the block size is 64. Your networks are .0, .64, .128 and .192. The address .100 sits in the .64 network, whose broadcast is .127 and whose usable range is .65 to .126. No binary was harmed.
Do twenty of these on paper and the pattern becomes automatic. Do them in your head on the bus and you will finish the exam section with time to spare.