doubt for word problem expert please understand my doubt

Question

OF means MULTIPLY but in normal english of has the meaning 'belonging to'

some of complex word problem i cant determine what is exact meaning of "of"
show me the key points that should help me to conclude the meaning "of" solving word problem

complex problem example
The digit in the units place of a number is equal to the digit in the
ten place of half of that number and the digit in the ten place of that
number is less than the digit in units place of half of the number by 1.
If the sum of the digits of the number is 7 then what is the number

tell me technique or steps for this doubt
please sir sort this problem

Answer 1

No rule, just experience and reasoning.

Two of a number:           2n

45% of x:                      0.45x

Tarzan of the the Jungle: no mupltiplication