Find K so that

integral of f(t)dt from [-1,x] + K = integral of f(t)dt from [3,x]

WORK

K = integral of f(t)dt from [3,x] - f(t)dt from [-1,x]

K = integral of f(t)dt from [3,x] + f(t)dt from [x,-1]

K = integral of f(t)dt from [3,-1]

Anti-derivative = 4x-(3/2)x^2

4x-(3/2)x^2 from [3,-1]

= -4

Let me know if my work is sound.