(2x-10)/21+(7x-4)/20=(2-x)/15+(8x+9)/4
60*(2x-10)/21+60*(7x-4)/20=60*(2-x)/15+60*(8x+9)/4
20*(2x-10)/7+3(7x-4)=4(2-x)+15(8x+9)
20*(2x-10)/7+21x-12=8-4x+120x+135
20*(2x-10)/7+21x-12=116x+143
20*(2x-10)/7=95x+155
4*(2x-10)/7=19x+31
7*4*(2x-10)/7=7*19x+7*31
4(2x-10)=133x+217
8x-40=133x+217
133x-8x=-40-217
125x=-257
x=-257/125