9/25 and 28/45 are both rather large numbers as denominators, so you can expect your LCD to be a bit large as well. the way i find the LCD is by trial and error. i take the biggest of the denominators and multiply it by low numbers (1, 2, 3, etc.) until i find one that works for both.
45*1 = 45, which 25 doesn't go into evenly
45*2 = 90, which when divided by 25, results in 3.6, aka not a whole number
45*3 = 135, which divided by 25 results in 5.4
45*4 = 180, which divided by 25 results in 7.2
45*5 = 225, which is promising because it ends with "25", and results in 9
so your LCD, which is divisible by both 45 and 25, is 225.
