Which expression is equivalent to 3x + 6y?

If the measure of xyz is 81 what is the measure of yz

The spotter on the ground is standing beneath the safety net. what is his distance from the base of the platform, to the nearest meter? 3 meters, 2 meters, 4 meters, 1 meter?

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?