3 per 4a x 4 per 5b=

[tex] \frac{3}{4a} \times \frac{4}{5b} \\ = \frac{(3 \times 4)}{(4a \times 5b)} \\ = \frac{12}{20ab}\\=\frac{3}{5ab}[/tex]
Maaf Kalau Salah

=3/4a x 4/5b
=3 x 4/4a x 5b
=12/20ab
=3/5ab