If the actual length of the bridge is 4200 feet, then what is the scale of the diagram of the bridge?

4200/6 = 700 not the answer

4200/5 = 840 is the answer

but the bridge measures 1 2 3 4 5 6 so you are trying to say that it should be 6 right but it is 5 ...

i. e. 1 unit is 840 ...

you see the scale that is 1 2 3 4 5 6 ...

840feet is distance between two units i. e. from 1 to 2 its 840, from 2 to 3 its 840, from 3 to 4 its 840, from 4 to 5 its 840 and from 5 to 6 its 840 ... so count how much 840's have come ... yeh thats 5 ...

So 5 * 840 = 4200 ... or 840 + 840 + 840 + 840 + 840 = 4200 ... you got that