$$(0)^2 = (25)^2 + 2a(50)$$ $$0 = 625 + 100a$$ $$-625 = 100a$$ $$a = -6.25 \text m/s^2$$
In an academic context, the term "solucionario" (solution manual) often refers to a separate book containing answers to a primary text's problems. However, the Schaum series itself functions as an integrated solution manual. $$(0)^2 = (25)^2 + 2a(50)$$ $$0 = 625