Express the equivalence relation in the following questions, and then solve the equation. (1) There are 36 willows in the park. Poplar is twice as big as willow. How many poplars and willows are there? Poplar+willow = total number solution: suppose there are x willows 2x+x = 36 3x = 36 x = 36/3x =12 (2) A house needs to be paved with square bricks.