Question 251667
Let x = number of passes completed
then
{{{12/20 = x/15}}}
multiplying both sides by 20:
{{{12 = 20x/15}}}
reducing the fraction on right:
{{{12 = 4x/3}}}
multiplying both sides by 3:
{{{36 = 4x}}}
dividing both sides by 4:
{{{9 = x}}}