Solve 105=frac{7*(a_{1}+21)}{2}

$$105 = \frac { 7 \cdot ( a _ { 1 } + 21 ) } { 2 }$$

Solve for a_1

$$a_{1}=9$$

Steps for Solving Linear Equation

Multiply both sides by 2.

$$105\times 2=7\left(a_{1}+21\right)$$

Multiply 105 and 2 to get 210.

$$210=7\left(a_{1}+21\right)$$

Use the distributive property to multiply 7 by a_{1}+21.

$$210=7a_{1}+147$$

Swap sides so that all variable terms are on the left hand side.

$$7a_{1}+147=210$$

Subtract 147 from both sides.

$$7a_{1}=210-147$$

Subtract 147 from 210 to get 63.

$$7a_{1}=63$$

Divide both sides by 7.

$$a_{1}=\frac{63}{7}$$

Divide 63 by 7 to get 9.

$$a_{1}=9$$