## Precalculus (6th Edition) Blitzer

$C=300$
To find out the solution we need to follow the four-step procedure: Step (1). As $C$ varies jointly with $A$ and $T$, we have $C=k\times A\times T$ Here $k$ is a constant. Step (2). Substitute $A=2100$ , $T=4$ and $C=175$ in $C=k\times A\times T$ to get the value of k. \begin{align} & 175=K\times 2100\times 4 \\ & K=\frac{175}{2100\times 4} \\ & K=\frac{1}{48} \\ \end{align} Step (3). Substitute the value of $k$ into the main equation. $C=\left( \frac{1}{48} \right)\cdot A\cdot T$ Step (4). Substitute $A=2400\,\text{ and }\,T=6$ to get: \begin{align} & C=\frac{1}{48}\times 2400\times 6 \\ & C=300 \\ \end{align}