Question 453283
Let {{{a}}} = the age of the Lincoln Memorial in 1985
Let {{{b}}} = the age of the Jefferson Memorial in 1985
given:
{{{ a = 1.5b }}}
{{{ a = b + 21 }}}
By substitution:
{{{ 1.5b = b + 21 }}}
{{{ .5b = 21 }}}
{{{ b = 42 }}}
and since,
{{{ a = b + 21 }}}
{{{ a = 63 }}}
1985 minus 63 years = 1922, the year
 the Lincoln memorial was built
1985 minus 42 years = 1943, the year the Jefferson
Memorial was built