1)$$4 cdot (a+3) = 4 cdot a + 4 cdot 3 = 4a + 12$$
2)$$5 cdot (10+m) = 5 cdot 10 + 5 cdot m = 50 + 5m$$
3)$$-10 cdot (-2m+3n) = -10 cdot (-2m) + (-10) cdot 3n = 20m - 30n$$
4)
5)$$5a(6a+3b) = 5a cdot 6a + 5a cdot 3b = 30a^2 + 15ab$$
6)$$-6x(5y-2x) = -6x cdot 5y - 6x cdot (-2x) = -30xy + 12x^2$$
7)$$(2a-5b+6c) cdot (-3) = 2a cdot (-3) -5b cdot (-3) + 6c cdot (-3) = -6a + 15b - 18c$$
8)$$(4x^3 + 7x^2 - x) cdot (-5) = 4x^3 cdot (-5) + 7x^2 cdot (-5) - x cdot (-5) = -20x^3 - 35x^2 + 5x$$
9)$$(2x^2-5x+3) cdot (-4x) = 2x^2 cdot (-4x) -5x cdot (-4x) + 3 cdot (-4x) = -8x^3 + 20x^2 - 12x$$