High low method

CA Co manufactures a single product and has drawn up the following flexed budget for the year.
60% 70% 80%
$ $ $
Direct materials 120 000 140 000 160 000
Direct labour 90 000 105000 120 000
Production overhead 54 000 58 000 62 000
Other overhead 40 000 40 000 40 000
Total cost 304 000 343 000 382 000

What would be the total cost in a budget that is flexed at the 77% level of activity?

Sir i wanted to know if I’m solving this question the correct way

Variable cost p.u: 382,000-304,000/8000-6000 because 80% and 60% activity = 39 variable cost pu

Fixed cost= 382,000-(8000×39)=70000

Total cost= 70000+(39×7700)=370300

Answer is correct, but did i do it the correct way sir? Or do i have to calculate every cost separately? Like material and labour are variable, production oh is semi variable, and other overhead are fixed