We have to write the system of equations.
The cost of 3 apples and 7 tangerines is $2.10.
If A is the price of the apples and T is the price of the tangerine, we can write:

We also know that 4 apples and 3 tangerines cost $1.85, so we can write:

The system of equations is then:

Answer: The equations of the system are 3A + 7T = 2.10 and 4A + 3T = 1.85.