So:

lg x =

= lg 1.25^30

= 30×lg 1.25 //: You can look up middle school students' math tables or use calculators.

= 30×0.0969 100 130080564 143587833 1582652 1

= 2.90730039024 16924307634994747956

x = 807.7935669463 1608874 16 1005084435

x≈807.79