The basic solar nebular disk model (sndm), developed by russian astronomer victor safronov, and was made available in english in the early
1960s
1970s
1860s
1870s

1970s

Explanation: The prevailing model for planetary acceleration also known as the fractal assembly dating back to 18th century assumes that the solar system is made up of small grains striking each other chaotically into bigger ones, to form planetesimals.

Plastesimals then collide to form planets. This model was proposed  by Russian astronomer Victor Safronov  and it was further translated in English in 1970s by George Wetherill.

This remained same for almost next 40 years.

a polymer is a chainlike molecule made up of small molecular units. these small molecular units are called monomers. monomers of polymer can be joined together either naturally or synthetically.  

9.9 years

a = p(1 + rt) . . account balance after time t at rate r starting with principal p

3000 = 2500(1 + 0.0202t) . . filling in the given numbers

1.2 = 1 + 0.0202t . . divide by 2500

0.2 = 0.0202t . . . subtract 1

0.2/0.0202 = t ≈ 9.901

it will take about 9.9 years for the account balance to reach $3000.