(5m-6)(3m+4)

You could use the FOIL algorithm, first inner outer last
15 m^2 + 20 m -18 m - 24 = 15 m^2 +2 m -24

Or you could multiply term by term and add
5m(3m+4) -6(3m+4)
= 15 m^2 + 20 m - 18 m - 24 = 15 m^2 + 2 m = 24
which we already knew