The area of the trapezoid is h * (a + b) / 2, where a and b are the bases of the trapezoid, h is the height of the trapezoid.
h trapezoid * (4 + 1) / 2 = 35 (according to the condition of the problem)
h = 35 / 2.5 = 14
Draw the height of the triangle ABC, as shown in the figure.
h of a triangle = h of a trapezoid, since they are both perpendicular to the same parallel bases of the trapezoid and form a rectangle.
S triangle = h triangle * BC / 2 = 14 * 1/2 = 7
Answer: S triangle = 7
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