The triangle's height would have to be 2 times that of the rectangles. To know this, you canlook at the formulas for the Area of each shape.
Rectangle: bh
Triangle: bh/2
A triangle is just a rectangle cut in half. In order for the areas to be the same asleep as the bases, the only way it can be true is if the height were 2 times larger than the height of the rectangle.