$78.90 = n(.05)+d(.10)

The below explanation can give you whatever you are seeking.

Step-by-step explanation:

The two unknowns in the equation are "n" and "d"

$78.90 = n(.05)+d(.10) ........................ (1)

Make both unknowns the subject of the formula and substitute for each other

............................ (2)

also

............................ (3)

You can substitute for either "n" or "d" in equation (1),

Putting equation (3) into (1)

78.90 = n(.05) +

78.90 = n(.05) + 78.90 - n( .05)

collecting all like terms

78.90 - 78.90 = n(.05) - n(.05)

0 = n(.05 - .05)

0/0 = n

n  is undefined

Putting equation (2) into (1)

78.90 =   + d(.10)

78.90 = 78.90 - d(.10) + d(.10)

78.90 - 78.90 = - d(.10) + d(.10)

0 = d (-.10 + .10)

0/0 = d

d is also undefined

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step-by-step explanation:

answer: c, the green line

step-by-step explanation:

there is no black line, eliminate b.

simple interest implies periodic payments, but the red line shows no payments, eliminate d.

simple interest has equal payments. if paid say every day, the graph is about a straight line (actually a stairstep).

the yellow line is not straight, eliminate a.

check: the green line is straight, answer is c.

simple interest with positive interest rate gives a straight line sloping up to the right. green line:

g(t) = $100 + ($200-$100) ÷ (20 years) × (t years)

= $100 + (4%/year) × ($100)(t years)

incidentally, the yellow line curving upward represents continuously compounded interest

y = $100 × 2^(t years / (14 assuming the yellow line hits $200 at 14 years. 2^0 is 1, so y(0) = $100; 2^(14/14) is 2, so y(14) = $200.