If you would like to know how much do two apples cost, you can calculate this using the following steps:
o ... the cost of one orange
a ... the cost of one apple
1 * o + 1 * a = $1.05
2 * o + 3 * a = $2.75
_______________
o + a = 1.05 ... o = 1.05 - a
2 * o + 3 * a = 2.75
2 * (1.05 - a) + 3 * a = 2.75
2.1 - 2 * a + 3 * a = 2.75
a = 2.75 - 2.1
a = $0.65
o = 1.05 - a = 1.05 - 0.65 = $0.4
2 * a = 2 * 0.65 = $1.3
The correct result would be: Two apples cost $1.3.