Object a moves with a constant velocity of -10 m/s and object b moves with a constant velocity of 5 m/s. which object has the larger speed?

Object A has the larger speed because speed is not a vector quantity, it is scalar. This means that directionality, or in this case the sign of the velocity, doesn’t matter.
Speed = |velocity|
Object a speed =|-10|=10 m/s
Object b speed =|5|=5 m/s

Object a is the answer.

Cpowerlifting my boi