Suppose a spaceship heading directly away from the Earth at 0.90c can shoot a canister (direction away from the Earth) at 0.70c relative to the ship. Take the shoot direction away from the Earth. (Take the direction away from Earth as negative). What is the ratio of its velocity as measured on Earth, to the speed of light?

Suppose a spaceship heading directly away from the Earth at 0.90c can shoot a canister (direction away from the Earth) at 0.70c relative to the ship. Take the shoot direction away from the Earth. (Take the direction away from Earth as negative). What is the ratio of its velocity as measured on Earth, to the speed of light?