In a laboratory, students were to do an experiment to find the elongation of springs. When one end of the spring is attached to a ceiling with an object of mass $'m'$ kg attached to the other end of the spring, the spring stretches to a length of $l$ centimeter as shown in the equation below. What is the value of $m$ when $l$ is $75$ ? <br> <br>$\qquad \qquad \qquad l = 21 + 2.5 m$

Question

$\begin{array}{1 1} (a)\; 19.6 \\ (b)\; 20.6 \\ (c)\; 21.6 \\ (d)\; 22.6 \end{array}$