Again, you've developed a linear demand model showing that QD $=50-4$P $+2$M$,$ and P $=15$ and M $=25.$ Goods with a negative income elasticity of demand are called inferior goods. Goods with a positive income elasticity of demand are normal goods, which are sometimes divided into necessities $($if income elasticity is less than $1)$ and luxuries $($if income elasticity is greater than $1).$ This good, at this price and income level, is$...$

an inferior good.

a necessity.

a luxury.

We don't have enough information to determine whether this good is inferior, a necessity, or a luxury.