B3. A cow and a calf together weigh $480 \mathrm{~kg}$. The ratio of their masses is 17 : 3.

A How much does the calf weigh?

B The calf gains $1.5 \mathrm{~kg}$ more each subsequent day than the previous day. In how many days will it reach a mass of $120 \mathrm{~kg}$?
B3 From the ratio of the cow's and calf's mass, we calculate the proportionality factor $\frac{480 \mathrm{~kg}}{20}=24 \mathrm{~kg}$. The mass of the calf is $24 \mathrm{~kg} \cdot 3=72 \mathrm{~kg}$. If the calf gains $1.5 \mathrm{~kg}$ per day, it will reach a mass of $120 \mathrm{~kg}$ in 32 days, which we calculate from the equation: $72+1.5 x=120 \Leftrightarrow x=32$.
A Calculation of the calf's mass: $\frac{480 \mathrm{~kg}}{20}=24 \mathrm{~kg}, 24 \mathrm{~kg} \cdot 3=72 \mathrm{~kg}$ ..... $1 \mathbf{t}$
Written answer, e.g.: The calf weighs $72 \mathrm{~kg}$. ..... $1 \mathbf{t}$
B Writing the equation $72+1.5 x=120$ and solving the equation $x=32$ ..... $2 \mathrm{t}$
Written answer, e.g.: The calf will reach a mass of $120 \mathrm{~kg}$ in 32 days. ..... $1 \mathrm{t}$