How much work lifts an 800 kg payload from the Earth's surface to a height of 3R (that is, 4R from…

Step 1. Exact. $W = \tfrac34 \times 800\ \text{kg} \times 9.8\ \text{m/s}^2 \times 6.4 \times 10^{6}\ \text{m} = 3.76 \times 10^{10}\ \text{J}$.

Step 2. Shortcut. $mgh = 800\ \text{kg} \times 9.8\ \text{m/s}^2 \times 1.92 \times 10^{7}\ \text{m} = 1.51 \times 10^{11}\ \text{J}$.