Question 144674
Let the two pieces of wood be y and z. Let x be the forearm

The system of equations is as :
{{{y = 3x -1}}}
{{{z = 5x + 15}}}


the graph is
{{{graph(600, 400, -10, 10 , -30, 10, 3x-1, 5x + 15)}}}



Is the answer reasonable? No. The value where to two plots meet yields {{{x=-8}}}

No one has a forearm that is negative in size.