please complete these problems without using built-in Matlab functions lu(), inv(), or A\b

12.15 Perform the same computation as in Sec. 12.2, but for the truss depicted in Fig. P12.15. FIGURE P12.15 400 200 145 45 30 . 12.2 If the input to reactor 3 in Sec. 12.1 is decreased 25 percent, use the matrix inverse to compute the percent change in the concen- tration of reactors 2 and 4