The garden workers planted trees along the side of the road, one tree every 4 meters, a total of 16 trees were planted. What is the distance from the first tree to the last tree?
园林工人沿公路一侧栽树，每隔4米栽一棵，一共栽了16棵．从第一棵到最后一棵的距离是多少米．
<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<result>60</result>