Answer: 11.2 Kg

According to Newton's second law, $\large\Sigma $$F = \overrightarrow{F1} + \overrightarrow{F2} + \overrightarrow{F3} = m\overrightarrow{a}$

$\Rightarrow \large\Sigma$$ F = (-2\overrightarrow{i}+ 2\overrightarrow{j})\; +(5\overrightarrow{i}-3\overrightarrow{j})\; + (-45\overrightarrow{i})\; $

$\Rightarrow \large\Sigma$$F =(-42\overrightarrow{i} -\overrightarrow{j})N$

$\Rightarrow |\Sigma F| = \sqrt{F_x^2 + F_y^2} = \sqrt{42^2+1^2} = 42.012\;N$

$\Rightarrow$ Mass $ = \large\frac{|\Sigma F|}{a} $$ = \large\frac{42.012\;N}{3.75 \;m/s^2}$$ = 11.2032\;Kg$