The local hardware store wants to increase their inventory. last year 15 electric screwdrivers cost them 300.how much would 45 screwdrivers cost

One way of doing this is to write the equation of ratios (15 screwdrivers / 45 screwdrivers) = ($300 / x).    Solve this equation for x.  To do this, you might try multiplying both sides of this equation by x to eliminate fractions.

Another way is to obtain the unit cost of each screwdriver and then multiply the result by 45 screwdrivers.