]. six pears and three apples cost $3.90. two pears and five apples cost $3.30. how much does one pear cost

Write the equation of the cost
p stands for the cost per pear, a stands for the cost per apple
6p + 3a = 3.9
2p + 5a = 3.3

Solve the equation system
To solve the equation system, we work on eliminating variable p so we will find the number of a. To eliminate, we have to change the coefficient of p to the same number (i will change it to coefficient 6)
6p + 3a = 3.9 (multiply 1)
2p + 5a = 3.3 (multiply 3)

6p + 3a = 3.9
6p + 15a = 9.9
- (substract)
      -12a = -6
           a = -6/-12
           a = 0.5

To find the cost per pear, subtitute the number of a to one of the equation
2p + 5a = 3.3
2p + 5(0.5) = 3.3
2p + 2.5 = 3.3
2p = 3.3 - 2.5
2p = 0.8
p = 0.4

The cost of one pear is $0.4