Since we know that the TOTAL distance from Kensington to Greenville is 4.3 km, and we also that the distance from Kensington to Springfield is 2.3 km, we can subtract these values to find the distance from Springfield to Greenville.
An expression does not have an equal sign. Since the value of a nickel is 5 cents and you want to find out the value of n nickels (which means if you had any number of nickels) the expression would be .05n