To find the simplest form of a fraction, you have to find the greatest common factor (GCF). To do so, list out the factors of the numerator (28) and the denominator (35) and find the biggest common number between the two numbers.
Factors of 28: 1, 2, 4, 7, 14, 28
Factors of 35: 1, 5, 7, 35
Out of those factors, we can see that 1 and 7 are the common factors, but 7 is the greatest which makes it our GCF.
Now we can divide the numerator and the denominator by the GCF to receive our simplest form.
28 ÷ 7 = 4
35 ÷ 7 = 5
Rewrite the fraction with the new numerator (4) and the new denominator (5).
The simplest form is: 4/5 or 0.8.