(X+30)/[(2X+30)/6]=X/[(2X+30)/10]
(X+30)*[(2X+30)/10]=X*[(2X+30)/6]
(X+30)*[2(X+15)/10]=X*[2(X+15)/6]
(X+30)*[(X+15)/5]=X*[(X+15)/3]
(X+30)*(X+15)/5=X*(X+15)/3
3(X+30)*(X+15)=5X*(X+15)
3(X2+45X+450)=5X2+75X
3X2+135X+1350=5X2+75X
2X2-60X-1350=0
X2-30X-675=0
(X-45)(X+15)=0
X=45或X=-15