B1. Write a linear function that has a zero at 4, and its graph passes through the intersection of the lines with equations $x-2 y-9=0$ and $2 x+y-3=0$.
B1. The intersection of the given lines is calculated by solving a system of two equations with two unknowns: $x-2 y-9=0$ and $2 x+y-3=0$. The solution to the system is the pair $x=3, y=-3$, and the intersection point is $P(3,-3)$. The graph of the desired linear function passes through this intersection point and through the point $A(4,0)$. We calculate its slope $k=\frac{0-(-3)}{4-3}=3$ and its y-intercept $n=0-3 \cdot 4=-12$, so we have the equation of the linear function: $f(x)=3 x-12$.

Correct solution of the system ....................................................................................................................... 1 point

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