It takes 20 min to walk from nus to buona vista mrt.

It takes 10 - 45 min by bus (95 or nuh shuttle) depending on luck, i.e. how fast the bus comes, traffic conditions and whether can squeeze onto the bus in the first place.

Taking a simple average, the average bus travel time is (10+45)/2=27.5 min. (No matter how unscientific, just take it as is. Proving the result is not required for exams.)

Travelling time can be reduced by timing the bus trips to reduce waiting time. However, this is not possible without knowledge of the bus schedule. (On top of that, even if you know the bus schedule, the nuh shuttle is rarely on schedule.)

The average time can be used to approximate the expected travelling time when the bus schedule is not known.

A simple comparison will show that the expected travelling time by bus is 7.5 min longer than on foot. (Please note that travel time on foot is relatively invariant and can be assumed to be a universal constant multiplied by an environment and situation dependent coefficient unique to every individual.)

Therefore, i conclude, in summary, it can be seen from the above evidence, that walking is the healthier choice since it raises your energy output significantly.

By the way, i was a fool. Still am, actually.