Consider the following binary linear programming formulation of a capital budgeting problem.

\[
\begin{array}{ll}
\text { Max } & 1,200 x_{1}+600 x_{2}+950 x_{3}+1,650 x_{4} \\
\text { s.t. } & 15,000 x_{1}+20,000 x_{2}+25,000 x_{3} \\
& +30,000 x_{4}<=70,000 \\
& x_{1}+x_{2}<=1 \\
& x_{4}<=x_{3} \\
& x_{1}, x_{2}, x_{3}, x_{4}=(0,1)
\end{array}
\]
The first cost of project \(x_{3}\) is

a. \(\$ 70,000\).

b. \(\$ 25,000\).

c. \(\$ 950\).

d. \(\$ x_{4}\).