I had 12 pencils my friend took 8 how many do I have now
It would take 20 min to wash so 20 times 6 120 then u add 60 bc there is 6 cars and it takes 10 min to dry each of them off
Multiply the fraction by 100%.

Without values for the other variables, I assume you're asking for a literal equation.
12y+d=-19y+t
31y+d=t
31y=-d+t
y=(-d+t)/31