Suppose you receive $$$$20,000$ advance today for your promising project from an investor. In addition, you expect to receive payment of $$90,000$ three years from now. However, for the maintenance of your project, you need to pay $$10,000$ now, $$50,000$ at the end of the second year and $$30,000$ at the end of third year. Using MARR is $10\%$ determine the approximate external rate of return $($ERR$).$

Question $3$ options:

a$)$

Between $0\mathrm{.}10$ and $0\mathrm{.}20$

b$)$

Between $0\mathrm{.}40$ and $0\mathrm{.}50$

c$)$

Between $0\mathrm{.}20$ and $0\mathrm{.}30$

d$)$

Between $0\mathrm{.}50$ and $0\mathrm{.}60$

e$)$

None of the answers are correct