1) 3m/m+5 - 8m/m^2+10m+25 = 3m/m+5 - 8m/(m+5)^2 = 3m^2+15m-8m/(m+5)^2 = 3m^2+7m/(m+5)^2 = m(3m+7)/(m+5)^2
2) m(3m+7)/(m+5)^2 : 3m+7/m^2-25 = m(3m+7)/(m+5)^2 * (m-5)(m+5)/3m+7 = m(m-5)/m+5
3) m(m-5)m+5 + 5m-25/m+5 = m^2-5m+5m-25/m+5 = m^2-25/m+5 = (m-5)(m+5)/m+5 = m-5