Use a piece of wood with a length of 8 decimeters to make a photo frame in the shape of an isosceles trapezoid. It is known that the length of the upper base of the trapezoid is 1 decimeter, the length of the waist is 2 decimeters, and how many decimeters is the length of the lower base?
用一根长8分米的木条做一个等腰梯形形状的相框，已知梯形的上底长1分米，腰长2分米，下底长多少分米？
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">8 - 1 - 4</gadget>
<output>3</output>

<result>3</result>