The lengths of the base and legs of an isosceles triangle are in the ratio of 3; 2 the perimeter of triangles is 105 find the length of the base

I guess you meam 3:2 instead of 3; 3
Anyhow,
The sides of isoceles triangle are leg, leg , base
each leg =2
while the base =4
To find the number you have to divide the ratio by total and multiply into 105
The base
3/7 × 105 = 45
The leg
2/7 × 105 = 30
Therefore, The length of the base = 45 cm