In order to determine the acceleration of the baseball, use the following expression for F (Newton second law):
F=m*a
where,
F: applied force = 154N
m: mass of the baseball = 0.42 kg
a: acceleration = ?
Solve the expression above for a, replace the values of the other parameters and simplify:
a = F/m
a = 154N/0.42kg
a = 366.67 m/s^2