Решение:

a) $$\frac{5y-3}{6y} + \frac{y+2}{4y} = \frac{2(5y-3) + 3(y+2)}{12y} = \frac{10y - 6 + 3y + 6}{12y} = \frac{13y}{12y} = \frac{13}{12}$$

б) $$\frac{3x+5}{35x} + \frac{x-3}{21x} = \frac{3(3x+5) + 5(x-3)}{105x} = \frac{9x + 15 + 5x - 15}{105x} = \frac{14x}{105x} = \frac{2}{15}$$

в) $$\frac{b+2}{15b} - \frac{3c-5}{45c} = \frac{3c(b+2) - b(3c-5)}{45bc} = \frac{3bc + 6c - 3bc + 5b}{45bc} = \frac{6c + 5b}{45bc}$$

г) $$\frac{8b+y}{40b} - \frac{6y+b}{30y} = \frac{3y(8b+y) - 4b(6y+b)}{120by} = \frac{24by + 3y^2 - 24by - 4b^2}{120by} = \frac{3y^2 - 4b^2}{120by}$$