Question 1012234
By the time firework a has been launched, firework b has already been launched for 0.25 seconds, so if we treat the two as equations, then
{{{a=220(t)}}}
{{{b=200(t)+200(0.25)}}}
And we want to know when these two equal eachother, as that's they will both detonate.
{{{220t=200t+200(0.25)}}}
{{{20t=50}}}
{{{t=2.5}}}