Franz Consulting started operations on January $1.$ During January, Franz consulting had $120$ hours of professional service. During February, the activity was $150$ hours. Consulting software subscription cost for these two levels of activity usage are as follows:

January February

Hours of professional service $120$ Hours $150$ Hours

Consulting software subscription cost $ $870$ $$1,050$

Use the high$-$low method to calculate the fixed component of the consulting software subscription cost.