Question 1205571
u, the ones digit
t, the tens digit
10t+u, the two-digit number


{{{system(t=u+4,10t+u=4tu-11)}}}, exact translation into symbolism


{{{10(u+4)+u=4u(u+4)-11}}}, substitution of t


{{{10u+40+u=4u^2+16u-11}}}

{{{11u+40=4u^2+16u-11}}}

{{{4u^2+5u-51=0}}}



{{{u=(-5+- sqrt(25+4*4*51))/(2*4)}}}

{{{u=(-5+- sqrt(841))/8}}}

{{{u=(-5+- 29)/8}}}

The PLUS 29 works.
{{{highlight(u=3)}}}
This means tens digit, {{{highlight(t=7)}}}.