For a very approximate answer just use ROC in fpm = % x TAS in kts
In this case 2.4 x 150 = 360 fpm
For a more accurate answer got to Section 3 MEP1 page 9 of your CAP698 and find the equation
Still Air % = (ROC / TAS) x (6000/6080)
This can be rearranged to give
ROC = (% x TAS x 6080) / 6000
In this case ROC = (2.4 x 150 x 6080) / 6000 = 364.8 fpm