$v_f = v_i + at$
$7.32 = v_o + 10a$ → equation (1)
$5.49 = v_o + 12a$ → equation (2)
Equation (1) minus equation (2)
$1.83 = -2a$
$a = -0.915 \, \text{ m/sec}^2$ answer
From equation (1)
$7.32 = v_o + 10(-0.915)$
$v_o = 16.47 \, \text{ m/sec}$ answer