Solve y=x-2 and x+y=12 using substitution

Part a : solve - vp + 40 < 65 for v . part b : solve 7w - 3r = 15 for r show your work!

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years

From the top of a tree a bird looks down on a field mouse at an angle of depression of 50°. if the field mouse is 40 meters from the base of the tree, find the vertical distance from the ground to the bird's eyes.