First, transform the height to SI unit (meter):
1 feet = 0.3048 m
12 feet = 12 x 0.3048 = 3.6576 m
For a vertical jump:
velocity = sqrt(2gh) = sqrt(2 x 9.8 x 3.6576) = 8.4669 meter/second
Therefore, at an angle of 45 degrees:
velocity = vertical velocity / sin(45)
= 8.4669 / sin(45)
= 11.974 meter/second