75 gm of sugar solution has 30% sugar in it. Then the quantity of sugar that should be added to the solution to make the quantity of the sugar 70% in the solution is :

Sugar in original solution = $$\frac{{75 \times 30}}{{100}}$$  = 22.5 gm
Let m gm of sugar be mixed.
$$\therefore \frac{{22.5 + {\text{m}}}}{{75 + {\text{m}}}} \times 100 = 70$$
⇒ 2250+ 100m = 75 × 70 + 70m
⇒ 2250 + 100m = 5250 + 70m
⇒ 30m = 5250 - 2250 = 3000
⇒ m = $$\frac{{3000}}{{30}}$$  = 100 gm