求合并一年级数学中的相似项(送分题！！！！！！！)

x-f+5x-4f =(1+5)x+(-1-4)f = 6x-5f

2a+3 b+6a+9 b-8a+12b =(2+6-8)a+(3+9+12)b = 24b

3pq+7pq+4pq+pq =(3+7+4+1)pq = 15pq

30a？b+2b？c-15a？b-4b？c=(30-15)a？b+(2-4)b？c=15a？b-2b？c

7xy-8wx+5xy-12xy =(7+5-12)xy-8wx =-8wx