`a)`
`( sqrt(4/3) + sqrt(25/3) - sqrt(3) ) . sqrt(3)`
`= sqrt(4/3) . sqrt(3) + sqrt(25/3) . sqrt(3) - sqrt(3) . sqrt(3)`
`= sqrt(4) + sqrt(25) - sqrt(9)`
`= 2 + 5 - 3 = 4`
`b)`
`( sqrt(5) + 2 sqrt(3) ) ( sqrt(5) - 2 sqrt(3) )`
`= ( sqrt(5))^2 - (2 sqrt(3))^2`
`= 5 - 12 = -7`