$(2)($a$)$ In class we showed a "slide" $($linked on the webpage as "cross sections"$)$ which at the bottom showed $p+p$ collisions at $450$GeV accelerator beam energy and claimed that for fixed$-$target collisions only $29$GeV of energy is actually available in the centerof$-$momentum system. Verify that. You'll find the formal solution that answers all such questions in the text, section $2\mathrm{.}7.$ Justify it in your answer.