Explanation:
Combine like terms
a. 2r + 3 + 4r = (2r + 4r) + 3 = 6r + 3
b. 8 + 3d + d = (3d + d) + 8 = 4d + 8
c. mn + (-3mn) + 6 = (mn - 3mn) + 6 = -2mn + 6
d. 10s + (-10) + (-4s) = (10s - 4s) - 10 = 14s - 10
Terms are called "like terms" if they have the same variable part (the same letters in the same powers). Like terms differ at most coefficient.