Calculate the total weight of 5 bags of grain (14 kg 250 g each) and the remaining oil (initial 13 L 650 mL, used 7 L 750 mL)?

1 kg = 1000 g
Weight of one bag = $14 \text{ kg } 250 \text{ g} = (14 \times 1000) \text{ g} + 250 \text{ g} = 14000 \text{ g} + 250 \text{ g} = 14250 \text{ g}$

Total weight = $14250 \text{ g} \times 5 = 71250 \text{ g}$

$71250 \text{ g} = 71000 \text{ g} + 250 \text{ g} = 71 \text{ kg } 250 \text{ g}$
The total weight of 5 bags is $\boxed{\text{71 kg 250 g}}$.

b) Remaining oil in the box

1 L = 1000 mL
Initial oil = $13 \text{ L } 650 \text{ mL} = (13 \times 1000) \text{ mL} + 650 \text{ mL} = 13000 \text{ mL} + 650 \text{ mL} = 13650 \text{ mL}$

Oil used = $7 \text{ L } 750 \text{ mL} = (7 \times 1000) \text{ mL} + 750 \text{ mL} = 7000 \text{ mL} + 750 \text{ mL} = 7750 \text{ mL}$

Remaining oil = $13650 \text{ mL} - 7750 \text{ mL} = 5900 \text{ mL}$

$5900 \text{ mL} = 5000 \text{ mL} + 900 \text{ mL} = 5 \text{ L } 900 \text{ mL}$
The remaining oil in the box is $\boxed{\text{5 L 900 mL}}$.

Question 7:

a) Place value of the digit 8 after the decimal point in 48.84

In the number 48.84, the first digit 8 is in the ones place. The second digit 8, which is after the decimal point, is in the tenths place.

The place value of the digit 8 in the tenths position is 0.8 or $\frac{8}{10}$.
The place value is $\boxed{\text{8 tenths}}$.