\(\leftrightarrow\)715(x-1986)+585(x-1989)+495(x-1996)+429(x-2007)=64350
\(\leftrightarrow\)715x-1419990+585x-116365+495x-988020+429x-861003=64350
\(\leftrightarrow\)2224x-4432578=64350
\(\leftrightarrow\)2224x=64530+4432578
\(\leftrightarrow\)2224x=4496928
\(\leftrightarrow\)x=2022


