The centre of a circle \( C \) is at the centre of the ellipse \( E : \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1, a > b \). Let \( C \) pass through the foci \( F_1 \) and \( F_2 \) of \( E \) such that the circle \( C \) and the ellipse \( E \) intersect at four points. Let \( P \) be one of these four points. If the area of the triangle \( PF_1F_2 \) is \( 30 \) and the length of the major axis of \( E \) is \( 17 \), then the distance between the foci of \( E \) is:
