Do the opposite of PEMDAS. First subtract b from both sides.
T = b + v²/2d
T (-b) = b (-b) + v²/2d
T - b = v²/2d
Multiply 2d to both sides
2d(T - b) = v²/2d(2d)
2d(T - b) = v²
Distribute 2d to both T and -b
2dT - 2db = v²
Isolate the v, root both sides
√(2dT - 2db) = √v²
v = √(2dT - 2db)
hope this helps