Stephen sells gin a bicycle for $138 and a helmet for $18. The total cost for gin is 130% of what Stephen spent originally to buy the bike and helmet how much did Stephen spend originally? How much money did he make by selling the bicycle and helmet to gin?

How to solve a simultaneous equation involved with fractions?

If f(x) = x+8 and g(x) = 4x- 3, find (f+g)(x)

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?