Find the LCD 4 and 28 :
Factor each denominator into its primes :
4 = 2²
28 = 2² * 7
Find the least common denominator 2² * 7 = 28
LCD = 28
[tex] \frac{3}{4} - \frac{1}{28} [/tex]
Adjust fractions based on the LCD :
[tex] \frac{3*7}{28} - \frac{1}{28} [/tex]
[tex] \frac{3*7-1}{28} [/tex]
[tex]= \frac{20}{28} [/tex]
Cancel common factor 4 :
[tex] \frac{20/4}{28/4} [/tex]
[tex]= \frac{5}{7} [/tex]
hope this helps!