A Boolean function $f$ of two variables $x$ and $y$ is defined as follows:
\[f(0,0)=f(0,1)=f(1,1)=1 ; \quad f(1,0)=0\]
Assuming complements of $x$ and $y$ are not available, a minimum cost solution for realizing $f$ using only $2$-input NOR gates and $2$-input OR gates (each having unit cost) would have a total cost of
- $1$ unit
- $4$ unit
- $3$ unit
- $2$ unit