Your title says Assembly program but what you have written is certainly not Assembler language, looks like C.
You have both a and b declared as integers but the result of (a * 1.25) will not be an integer so you need to declare b as a different type.
You need to initialize a to the number you want to increase by 25%. I see that your statement says the program is supposed to read a number. Should it read the number from a file or read it from the console? You need to add code to read that number from wherever and assign it to the variable a.
Your printf line is incomplete, google printf to find out what is missing.