What is an equation with more than one operation called

If you could answer these your a life saver

The nth term of a sequence in 2n-1 the nth term of a different sequence is 3n+1 work out 3 numbers that are in bothe sequences and are between 20 and 40

Afamily has two cars. the first car has a fuel efficiency of 25 miles per gallon of gas and the second has a fuel efficiency of 15 miles per gallon of gas. during one particular week, the two cars went a combined total of 1025 miles, for a total gas consumption of 55 gallons. how many gallons were consumed by each of the two cars that week?