Question 435799
Let {{{a}}} = number he killed on Monday
Let {{{b}}} = number he killed on Tuesday
{{{ a = 2b + 3 }}}
{{{ a + b = 9 }}}
------------------
By substitution:
{{{ 2b + 3 + b = 9 }}}
{{{ 3b = 9 - 3 }}}
{{{ 3b = 6 }}}
{{{ b = 2 }}}
and
{{{ a + b = 9 }}}
{{{ a = 7 }}}
He killed 7 frogs on Monday