5t=v-u (Subtract u on both sides)
t=(v-u)/5 (Divide by 5 in both sides)
To solve this all you need to do is do the opposite of multipulcation:
1590/5
Which equal 318. To check you answer do 318×5
Step-by-step explanation:
85 is the answer you are looking for

the equation is a quadratic one, and it has a positive coefficient on the leading term, meaning, is opening upwards, so it has a "burrow" for the vertex.
the minimum or lowest point for a quadratic opening upwards is, well, the vertex point :), the "x" value is the year, the "y" or f(x) value is the population, we're asked for the year, or the x-coordinate of the vertex
well