What expression is equivalent to 13-(-21)

If jm equals 5x -8 and lm equals 2x -6 which expression represents jl

If f(x)=-x^2+6x-1 and g(x)=3x^2-4x-1,find(f+g)(x)

A33 gram sample of a substance that's used to detect explosives has a k-value of 0.1473. n = noekt no = initial mass (at time t = 0) n = mass at time t k = a positive constant that depends on the substance itself and on the units used to measure time t = time, in days