Question 242417
The perimeter equals to the sum of two widths and two lengths.  The generic formula would be: {{{p=2w+2l}}}
Let p=perimeter, w=width, and l=length.
Since p=1280, and w=l-90, we can say:
{{{1280=2(l-90)+2l}}}
Let's solve for l...
{{{1280=2l-180+2l}}}
{{{1280+180=2l+2l}}}
{{{1460=4l}}}
{{{1460/4=l}}}
{{{l=365}}} <--- one lenght measures 365 miles
.
Let's find the width:
{{{w=l-90}}}
{{{w=365-90}}}
{{{w=275}}} <--- one width measures 275 miles
.
Let's check our answers by plugging them in the original equation.
Remember: {{{1280=2(l-90)+2l}}}
{{{1280=2(365-90)+2(365)}}}
{{{1280=(2*365)-(2*90)+(2*365)}}}
{{{1280=730-180+730}}}
{{{1280=1280}}}
.
Done with the first problem!
.
Second problem: {{{3(t-2)>=9(t+2)}}}
First, we need to distribute (multiply) 3 and 9 by the contents in the parenthesis.  Then we will solve for t.
.
{{{3(t-2)>=9(t+2)}}}
{{{3t-(3*2)>=9t+(9*2)}}}
{{{3t-6>=9t+18}}}
{{{3t-9t>=18+6}}}
{{{-6t>=24}}}
Now we need to divide by -6 on both sides of the inequality.  Remember that when we multiply or divide a negative number in an inequality, the symbol changes direction.  Notice the change below:
{{{t<=24/-6}}}
{{{t<=-4}}}
.
Done with the second problem!