Упростите выражения 8а^2b:(4ab)+15ac^2:(5c^2) 7.5x:2y^2:(3x^2y)-3.9my:(12m)...

1) $\frac{8 a^{2}b }{4ab}+ \frac{15ac ^{2} }{5c ^{2} } = 2a + 3a = 5a$
2) $7,5x : 2 y^{2} : 3 x^{2} y - \frac{3,9my}{12m} = \frac{7,5x}{2 y^{2} *3 x^{2} y} -0,325y = \frac{1,25}{x y^{3} } - 0,325y$
3) $\frac{2,1a b^{2} }{ \frac{4}{3} b^{2} } - \frac{2,7a t^{3} }{ \frac{8}{9} t^{3} } = 1,575a - 3,0375a= - 1,4625a$
4) $\frac{6 \frac{1}{4} c^{2}d }{2 \frac{1}{2}cd } + \frac{8 \frac{1}{4} c^{2} t^{2} }{5 \frac{1}{2}c t^{2} } = 2,5c + 1,5c = 4c$