Please help
Solve log x=4.

How many $20 bills do you need to have to make $280

Solve the following pair of equations for x and y: ax/b_ by /a= a +b; ax - by = 2ab

The number of calories you burn depends on your weight. a 110-pound person burns 163 calories during 30 minutes of tennis. find the number of calories that a 190-pound person would burn during the same activity, assuming they burn calories at the same rate.