Two of the numbers were switched in a multiplication equation, so the answer would be commutative- multiplication.
Ok, so 120 pages plus the 60% of the book she has left to read will give the total number of pages.
That means that 120 pages is 40% of the book.
Make a proportion
120/40% = x/60%
72 = .4 x
x = 180 pages
The circumference is about 3.14 (

) times bigger than twice the radius. Mathematically, this can be writted as

, where C equals the circumference and r equals the radius, or

where C equals the circumference and d equals the radius.