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Let R and A be the prices for one oRange and one Apple at the supermarket, respectively.
Then from the condition you have this system of equations
3R + 5A = 2.05 (1)
3R + 5*(1.5A) = 2.55 (2)
Simplify it
3R + 5A = 2.05 (1)
3R + 7.5A = 2.55 (2)
To solve this system, apply the Elimination method.
For it, subtract equation (1') from (2'). You will get
2.5A = 0.50
A =
= 0.2.
Then from (1), 3R + 5*0.2 = 2.05, 3R = 2.05 - 1 = 1.05, R = 1.05/3 = 0.35.
Solved.