Question 683682
Let {{{ y }}} = the age of the younger person
Let {{{ x }}} = the age of the older person
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I can put the equation into the form
{{{ y = m*x + b }}}
I can say
(1) {{{ 3 = m*57 + b }}}
I can also say
(2) {{{ 0 = m*54 + b }}} ( older person was 54 when younger person was born )
(2) {{{ b = -54m }}}
and
(1) {{{ 3 = 57m -54m }}}
(1) {{{ 3m = 3 }}}
(1) {{{ m = 1 }}}
and
(2) {{{ b = -54m }}}
(2) {{{ b = -54 }}}
So, the equation is
{{{ y = x - 54 }}}
Here's the plot
{{{ graph( 400, 400, -5, 100, -5, 70,  x - 54 ) }}}