Determine whether (4, -2) is a solution of y= -3/4x what the answer or solution

Element x decays radioactively with a half life of 8 minutes. if there are 450 grams of element x, how long, to the nearest tenth of a minute, would it take the element to decay to 37 grams?

If 1/√5+1/√5+1=p+q√r , find the values of p, q and r

How to do this , and can some one explain