Answer:
715 mL
Explanation:
You want the total volume in two containers that have the volume ratio 4:7 and a difference in volumes of 195 mL.
Ratio units
Considering the question in terms of "ratio units," we see the difference of ratio units is 7-4 = 3, and the total of ratio units is 7+4 = 11. Then the total volume will be 11/3 times the difference in volume:
total volume = (11/3)(195 mL)
total volume = 715 mL
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Additional comment
Though it is not necessary, as a check you can work out the volumes of the containers. The smaller will be 4/3 times the difference: 260 mL, and the larger will be 7/3 times the difference: 455 mL. The total is ...
455 +260 = 715 . . . mL
and the difference is ...
455 -260 = 195 . . . mL
If you prefer to work with equations for the volume, you can let x and y represent the volumes of the smaller and larger containers. Now you have ...
x/y = 4/7
y -x = 195
Substituting for y gives ...
x/(195 +x) = 4/7
7x = 4(195) +4x
3x = 4(195) ⇒ x = (4/3)·195 . . . . as above
Then the total volume is ...
x+y = 195 +2x = 195(1 +2·4/3) = 11/3·195 . . . as above