A uniform electric field of 4.50 kN/C points in the +x direction. 1)What is the change in potential energy of a +2.

A uniform electric field of 4.50 kN/C points in the +x direction.

1)What is the change in potential energy of a +2.00 nC test charge, Uelectric, b - Uelectric, a, as it is moved from point a at x = -30.0 cm to point b at x = +50.0 cm? (Express your answer to two significant figures.)

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How can one approach this question?

I tried it and got 7.2  but it is not the correct answer.