Each session should take approximately one and a half hours.
Explanation:
The correct sentence that properly uses words to express numbers is option B because the numbers expressed as words "1.5" is correctly written as "one and a half hours".
The other options do not correctly use words to express numbers. Option A needs to be written in numbers format, "21st April or April 21", Option C also needs to be written in number format "$25" and Option D also needs to be written in number format "1st seminar".
