Can someone explain how to find two positive numbers such that their product is 192 and the sum of the first plus three times the second is a minimum?

If f(x)=x^3 and g(x)=2x+7 when g(x)=-5

Write the fraction or mixed number and the decimal shown by the model

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling