You have charts for FL240 and FL300 and FL270 is halfway between them.

At FL240 the two winds on track are approx 210/55 and 230/55 giving a mean of 220/55.

At FL300 the two winds on track are both about 230/80.

At FL270 the wind will be the mean of 220/55 & 230/80 = 225/70 so 220/70 is the best answer.

OR

Since the mean wind speed is 70kts you have the choice of 220/70 or 270/70 and it isn't 270/70 just by looking at it.