First you need to simplify the ratio so divide 3 by 5, to come out with 1:0.6. Then solve for the unknown then add the unknown to the known for the sum
I like to solve these by graphing, so if you graph both of these functions (as shown in the picture below), you look for the intersection between the two graphs, which in this case is (-2,6).
First on is linear, second is exponential, third is exponential and the last is linear All problems that are linear increase by a constant rate, ones that increase exponentially increase by a percentage or decimal