Is a triangle with sides of 9 meters, 12 meters, and 15 meters a right triangle? explain

Leo has b boxes of pencils. each box contains 6 pencils. he has a total of 42 pencils. the equation that represents this situation the value of b that makes the equation true the first one is b+6=42,6b=42,b=42+6,or 42b=6 the second one are 7,836 48

Ineed if you could explain and give me the answer you! this needs done

If f(x) =3x-2 and g(x) =2x+1 fins (f+ g) (x)