Samir buys x cans of soda at 30 cents each and (x+4) cans of soda at 35 cents each. the total cost was $3.35. find x

0.30x is the cost of the first type of soda. 0.35(x+4) is the cost of the second type of soda. Put these into an equation looking like:

Cost of Soda A + Cost of Soda B = Total Cost
0.30x + 0.35(x+4)=3.35 --> Expand 0.35(x+4)
0.30x + 0.35x + 1.4 = 3.35 --> Add the x's and subtract 1.4
0.65x = 1.95 --> Divide by 0.65
x = 3

Samir buys 3 cans of soda at 30 cents each and 7 (3+4) cans of soda at 35 cents each. Samir buys a total of 10 cans of soda.