Answer:
$ 388.77
Explanation:
First, let's change the annually interest(ia) for monthy (im):
(1+ im)¹² = 1 + ia
(1 + im)¹² = 1 + 0.04125
1 + im =

1 + im = 1.00337
im = 0.00337
im = 0.337%
The total amount (A) of the investment can be calculated by:

Where R is the amount invested by month, n is the number of months, and i is the interest.
10 years = 10*12 = 120 months

50,000= R*147.59
R = $ 388.77