optimization calculus

Question

An apple farm yields an average of

40

bushels of apples per tree when

26

trees are planted on an acre of ground. Each time 1 more tree is planted per​ acre, the yield decreases by 1 bushel​ (bu) per tree as a result of crowding. How many trees should be planted on an acre in order to get the highest​ yield?

Answer 1

t repressents the number of tree increase

Y(t) = (40 - t)(26 + t)

Can you convert to vetext form and determine maximum?