Question 278427
Let A = 30 sec. Commercial
Let B = 60 Sec. Commercial

*Note I am using Minutes in my equations and not seconds ( 1 min = 60 sec)

Equation 1: {{{A + B = 16}}}
Equation 2: (((0.5A + B = 13}}}

Solution:
------------------
Solve equation 1 for one of the variables. I will solve for B
Equation 1: {{{A + B = 16}}}
{{{B = 16 - A}}}
Now plug (16 - A) into equation 2 for B
Equation 2: (((0.5A + B = 13}}}
(((0.5A + (16 - A) = 13}}} Simplify
{{{0.5A + 16 - A = 13}}} Combine like terms
{{{-.05A + 16 = 13}}} Subtract 16 from both sides
{{{-0.5A = -3}}} Divide both sides by -0.5
{{{highlight(A = 6)}}}

Now find B by plugging 6 into equation 1 for A
Equation 1: {{{A + B = 16}}}
{{{6 + B = 16}}}
{{{highlight(B = 10)}}}

Check your answer:
-------------------
Plug your values into equation 2 and see if it checks out.
Equation 2: (((0.5A + B = 13}}}
(((0.5*(6) + 10 = 13}}}
{{{3 + 10 = 13}}}
{{{highlight(13 = 13)}}}