question A is just filling in both numbers and showing one is in the minus and the other one is at + so you prove it i between 3 and 4 (-0.21816;0.0183)
question B is just fill X1 in at Xn thus resulting in Xn+1 which is X2 than fill it in again and get X3, X2= 3.8801, X3 = 3.9178
question C got no diagram but just find the points you calculated up there^^ and you go