I've done 95% of this. I just don't get one specific part. General cal physics

[randoreds]

Homework Statement

A fish is swimming in a horizontal place has velocity of ( vi = 4.00i + 1.00j) ms at a point in the ocean where the position relative to a certain rock is ri=(10.i- 4.00j)m. After the fish swims with constant acceleration for 20 s, it velocity is v = 20.0i -5.00j. Question C) what is the position at 25 s, if at a constant velocity.

Homework Equations

Δd= vit+ 1/2at^2

The Attempt at a Solution

Ok part a) so the components of V are .79 in the X direction and -0.3 in the Y direction. part b) was you had to find the direction of the vector with respect to the x-axis it is 339degree sign. But for part C, I'm solving for Xf and Yf.
Xf = (4.00) (25) + (1/2) (.79)(25)^2 (-- This is wrong. I checked the solution in the back. and the only difference is 10. I think it has to do with the rock. for some reason they randomly added the position of the Rock. So my question is why? Because when I was solving for the components(part A), I didn't need to add the position of the rock. And I got the right answer! Any help would be appreciated

 

[randoreds]

And my question is more, how would you know to do this? (if I encounter this doing other problems)

 

[NasuSama]

Homework Statement

A fish is swimming in a horizontal place has velocity of ( vi = 4.00i + 1.00j) ms at a point in the ocean where the position relative to a certain rock is ri=(10.i- 4.00j)m. After the fish swims with constant acceleration for 20 s, it velocity is v = 20.0i -5.00j. Question C) what is the position at 25 s, if at a constant velocity.

Homework Equations

Δd= vit+ 1/2at^2

The Attempt at a Solution

Ok part a) so the components of V are .79 in the X direction and -0.3 in the Y direction. part b) was you had to find the direction of the vector with respect to the x-axis it is 339degree sign. But for part C, I'm solving for Xf and Yf.
Xf = (4.00) (25) + (1/2) (.79)(25)^2 (-- This is wrong. I checked the solution in the back. and the only difference is 10. I think it has to do with the rock. for some reason they randomly added the position of the Rock. So my question is why? Because when I was solving for the components(part A), I didn't need to add the position of the rock. And I got the right answer! Any help would be appreciated

More likely you will need to use just vectors for the equation to determine the answer. Don't find the diagonal components yet!