1)
4m⁴a / 6x² * 2x² / 4m³a² = m / 3a.
2)
m / 3a : (10+2a) / 6a² = m / 3a * 6a² / (10+2a) = 2am / (10+2a).
3)
2am / (10+2a) * (a²-25) / 2m² = 2am / (2(5+a)) * (a-5)(a+5) / 2m² = a(a-5) / 2m.
4)
a(a-5) / 2m : (a²-10a+25) / 6m = a(a-5) / 2m * 6m / (a²-10a+25) =
= a(a-5) / 2m * 6m / (a-5)² = 3a / (a-5)