$$n + ^{235}_{92}U \rightarrow ^{144}_{Z}Ba + ^{A}_{36}X + 3n,$$
From law of conservation of atomic number
$$0 + 92 = Z + 36$$
$$\Rightarrow Z = 92 - 36 = 56$$
From law of conservation of mass number,
$$1 + 235 = 144 + A + 3 \times 1$$
$$A = 236 - 147 = 89$$