when running a line, in a right-triangle, from the 90° angle perpendicular to its opposite side, we will end up with three similar triangles, one Small, one Medium and a containing Large one, from where we can use proportions to get their sides, so Check the picture below.
The greatest common factor of 12 and 6 is 6.
There are 2 ways to do this. I'm going to do it the way that I think is most simple.
You have to find their LCM which is 40. Now times 40 to 1/4 v and 7/10
The equation then becomes 10+40v=28
You simplify it: 40v=18
v= 9/20