Ivan Kuckir's solution is correct, I'm just adding an explanation as it might help someone later.
Explanation - Tint means adding white to a colour.
Tint %X implies = there is a mixture of white and your color where white is (100-X)% of the mixture and your color constitutes X% in the mixture.
Thus, say for color Red (255,0,0) and tint .6 => Create a mixture with 60% RED and 40% WHITE.
Hence, the resulting mixture should be something like -
.6 * RED + .4 * WHITE
This can be followed for mixing any 2 colors (C1, C2) in a certain proportion = p:q
new R = p/(p+q) * R1 + q/(p+q) * R2
new G = p/(p+q) * G1 + q/(p+q) * G2
new B = p/(p+q) * B1 + q/(p+q) * B2
For tint, (R2,G2,B2) = (255,255,255)
new R = tint*R + (1-tint)*255;
new G = tint*G + (1-tint)*255;
new B = tint*B + (1-tint)*255;