$10000+1000t=8000+3\cdot 2^t$

$2000+1000t=3\cdot 2^t$

$1000(2+t)=3\cdot 2^t$

$3+\log_{10}(2+t)=\log_{10}(2)t+\log_{10}(3)$

$3+\log_{10}(2+t)-\log_{10}(3)=\log_{10}(2)t$

$3+\log_{10}\left(\dfrac{2+t}{3}\right)=\log_{10}( 2)t$

$t=\dfrac{3+\log_{10}\left(\dfrac{2+t}{3}\right)}{ \log_{10}(2)}$