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first off, lets define our variables f = number of hours worked by the first mechanic s = number of hours worked by the second mechanic, with me so far?
actually, let me make a quick correction
f = the rate charged by the first mechanic s = the rate charged by the second mechanic
anyway, it says that the sum of the rates is $190 so f + s = 190, with me so far?
now, it says that they charged 3225 together, total so now, we can write another equation first mechanic money + second mechanic money = 3225
so, now we can write an expression to figure out how much each mechanic made the first mechanic worked 20 hours, so he charges: 20f the second mechanic worked 15 hours, so he charges: 15s
that gives us two equations: f + s = 190 20f + 15s = 3225 solve for f and s
start by multiplying the first equation by 20