Step-by-step explanation:
m= 12 and n = 3
[tex]a. \: \frac{m}{3} + 5n \\ \frac{12}{3} + 5 \times 3 = 4 + 15 = 19[/tex]
[tex]b. \frac{ mn}{4} = \frac{12 \times 3}{4} = \frac{36}{4} = 9[/tex]
c.[tex]3m - 12n \\ \\ 3 \times 12 - 12 \times 3 = 36 - 36 = 0[/tex]
