[tex]\frac{16a^6c^4}{48ac}=\frac{16a^{6-1}c^{4-1}}{16*3}=\frac{a^5c^3}{3}\\\\\frac{25a(a-b)}{40b(a-b)}=\frac{5*5a}{5*8b}=\frac{5a}{8b}[/tex]