The solution is where the red line crosses the blue line, which on the X axis is between the 1 and the 2, so about 1.5.
Convert the fractions to decimal and see which one is close to 1.5:
13/8 = 1.625
25/16 = 1.5625
7/4 = 1.75
27/16 = 1.6875
The closest one to 1.5 is 25/16