The Garden Bureau designed a rectangular field with two kinds of grasses of different shades. The dark grass forms a letter pattern, and the light grass serves as the background. If it forms a "T" shape, the dark grass occupies 35 square meters; if it becomes an "F" shape, the dark grass occupies 50 square meters. Assuming that the direction of the letters is the same, the width of the grass strip is the same, and each horizontal and vertical stroke reaches the maximum, then how many square meters does the dark grass occupy when forming an "E" shape?
园林局设计用颜色深浅不同的两种草铺一块长方形的场地，深色的草形成字母图案，浅色的草作为背景．若成"T"字形，深色的草占35平方米；若成"F"字形，深色的草占50平方米．假定字母的方向一致，草带的宽度相同，每一横竖笔画都达到最大，那么成"E"字形时深色的草占的面积是多少平方米．
<gadget id="calculator">50 - 35</gadget>
<output>15</output>

<gadget id="calculator">50 + 15</gadget>
<output>65</output>

<result>65</result>