Find the line integral:

∫C(2y2 i + x j) · dr , where C is the line segment from (3,1) to (0,0).

My answer so far (...which has gone awfully awry. the answer is supposed to be -7/2):

y = 1/3x

x = 3y

0 ≤ t ≤ 3

∫ (lower limit: t=0 upper limit: t=3) (2t^2i + tj) · (-3i-j) dt

∫ (lower limit: t=0 upper limit: t=3) (-6t^2 - t) dt

= -6(1/3)t^3 - (1/2)t^2 , evaluated from 3 to 0

= -2t^3 - (1/2)t^2 , evaluated from 3 to 0

= [-2(27) - (9/2)] - [0]

= -54 - 9/2

= -108/2 - 9/2

= -117/2 (...which is far off from the correct answer above. I am pretty sure I messed up the parameterization. anybody, please help?)

(this is schoolwork, so only helpful hints and enlightening explanations, please, not just correct answers. thanks.)