Add. 7/4+9/-5 wrote your answer as a fraction in simplest form

7/4 + 9/-5 =

Since the denominator of the second fraction is negative the sign will change from negative to positive

We will get

7/4 - 9/5

First find the LCM

LCM of 4 and 5 is 20

7/4 - 9/5 = 5(7) - 4(9)/ 20

Simplify

We get

35 - 36/20

= -1/20

Hope this helps

-1/20

Step-by-step explanation:

7/4 + -9/5

We need a common denominator, which is 20

7/4 *5/5   + -9/5 *4/4

35/20  + -36/20

Add the numerators together

-1/20

To obtain the quadratic equation for the data set given, i have used excel spread sheet, this is shown in the attachment below. the equation is: y=-0.4931x²+23.38x+996.03b]the density of the sample at depth of 20 m will be : f(20)=-0.4931(20)²+23.38(20)+996.03f(20)=1266.39