Question 946597
Use a substitution,
{{{u=4t-5}}}
.
.
.
{{{u^2-10u+21=0}}}
{{{(u-7)(u-3)=0}}}
Two solutions:
{{{u-7=0}}}
{{{u=7}}}
{{{4t-5=7}}}
{{{4t=12}}}
{{{t=3}}}
and
{{{u-3=0}}}
{{{u=3}}}
{{{4t-5=3}}}
{{{4t=8}}}
{{{t=2}}}