✓ Mathematica : cpu = 0.0091341 (sec), leaf count = 39
DSolve[{t*Derivative[1][x][t] == -t + 2*x[t], t^3*Derivative[1][y][t] == t - x[t] + t^2*y[t], t^4*Derivative[1][z][t] == t - x[t] - t^2*y[t] + t^3*z[t]},{x[t], y[t], z[t]},t]
✓ Maple : cpu = 0.079 (sec), leaf count = 37
dsolve({t*diff(x(t),t) = 2*x(t)-t, t^3*diff(y(t),t) = -x(t)+t^2*y(t)+t, t^4*diff(z(t),t) = -x(t)-t^2*y(t)+t^3*z(t)+t})