how

21.

The perimeter of a triangle =  the sum of the sides

So.....we need to solve this

x + ( x + 3)  + (x + 5)   = 26

Can you take it from there, critical ???   [ P.S......if so....post your answer and  I'll check it  ]

22.

Mmmm...this is a more interesting problem  !!!

The radiator holds 480  oz of fluid and leaks at 4 oz / min

So...the number of minutes it takes to  drain is  just  480  / 4   = 120  minutes  = 2  hrs

Since the truck travels at 35 mph...the distance it travels before the radiator is empty  is

35 mph x 2 hours  =   70  miles

21. 6