Roman, bob and roger buy red and green marbles. red and green marbles don't have the same price. roman pays 70 cents for four red marbles and two green marbles. bob pays 95 cents for two red marbles and five green marbles. how much will roger pay if he buys one red marble and one green marble

Ok so let the price for 1 red marble be R, and the price of one green marble be G.
We know Roman paid 70 cents for 4 red and 2 green marbles, so 4R + 2G = 70
We also know Bob paid 95 cents for 2 red and 5 green marbles, so 2R + 5G = 95.
However, if Bob bought double of each kind of marble, he would inevitably pay double as well, so 4R + 10G = 190
So if you subtracted the equations,
(4R+10G) - (4R+2G) = 190 - 70
So 8G is 120
G = 15
So a green marble is 15 cents.

Sub this back in:
4R + (2x15) = 70
4R = 40
R = 10
So a red marble is 10 cents.

So of Roger buys one of each, he pays 10 + 15 = 25 cents
Hope this helped