obtain explicit solutions from "solve"

edit

I tried to use "solve" but, in the output, the variable of my interest is left implicit

[x3 == 1/6780*(27360*a + 9618*t - sqrt(202500*t^2*x3^2 + 1464480000*a^2 + 541225440*a*t + 17122609*t^2 + 22500*(528*a*t + 7*t^2)*x3 - 26040*sqrt(324*t^2*x3^2 + 20736*a^2 + 2016*a*t + 49*t^2 + 36*(528*a*t + 7*t^2)*x3)*(240*a + 13*t)) - 25*sqrt(324*t^2*x3^2 + 20736*a^2 + 2016*a*t + 49*t^2 + 36*(528*a*t + 7*t^2)*x3))/t, x3 == 1/6780*(27360*a + 9618*t + sqrt(202500*t^2*x3^2 + 1464480000*a^2 + 541225440*a*t + 17122609*t^2 + 22500*(528*a*t + 7*t^2)*x3 - 26040*sqrt(324*t^2*x3^2 + 20736*a^2 + 2016*a*t + 49*t^2 + 36*(528*a*t + 7*t^2)*x3)*(240*a + 13*t)) - 25*sqrt(324*t^2*x3^2 + 20736*a^2 + 2016*a*t + 49*t^2 + 36*(528*a*t + 7*t^2)*x3))/t]

Someone can help me? Thank you,

Carlo