Question 179292
Let {{{a}}}= Joan's age
Let {{{b}}}= Jim's age
given:
(1) {{{4a + 3b = 47}}}
(2) {{{b = 2a - 1}}}
substitute {{{b}}} in (2) 
for {{{b}}} in (1)
(1) {{{4a + 3b = 47}}}
{{{4a + 3*(2a - 1) = 47}}}
{{{4a + 6a - 3 = 47}}}
{{{10a = 50}}}
{{{a = 5}}}
And, since
(2) {{{b = 2a - 1}}}
{{{b = 2*5 - 1}}}
{{{b = 9}}}
Joan is 5 and Jim is 9