When we solve for d (total distance), don't we need to divide total d by 2 to get the ACTUAL distance to his job—not round trip? Maybe I am misinterpreting, but the question asks for the distance to his job (if the question wanted 'round trip', shouldn't it ask 'what is the total distance travelled?'
In the answer explanation, we set d = distance to work. So "d" is the one-way distance; therefore, when we eventually solve for d, we don't need to divide it by two.
We expressed the time to work as d/45 and the time back from work as d/60 and made the equation:
d/45 + d/60 = 2
When we solve, we get d = 360/7, the distance between David's home and work.