The correct answer of the given question above would be 8ft/sec. The minimum speed that the stone be thrown so as to reach a height of 49 feet is 8ft/sec. Consider this given solution here:
u^2 = 2x a x 1
u^2 = 2 x 32 x 1
u = 8 ft/sec
Hope this answer helps and this is what you are looking for.
